Theory:

Jim: That’s just why I came. Amy, I think I’ll look up a lantern and...

Betty: (interrupting) I’ve got a flashlight. I’ll get it and some candles.

Rose: (from outside still at the telephone, with irritation): Central Central! I’m trying to get Main 3022—I can’t – (There is a pause and Rose comes to the door, her face frightened.) The telephone is dead! I can’t get Central. There isn’t even a buzzing on the line!
 
Jim: Means the lines are down between here and town! Well, girls, let’s get organized! Betty, look up your flashlight and candles, lamps, lanterns or anything you’ve got. Rose, fill the tubs and pails and Amy and I will check on food, blankets and coats. Better get out the first-aid kit. Everyone make it snappy! (Rose and Betty exit left. Jim turns to Amy.) This is serious. Amy, I don’t want to scare you, but your house is in the direct line of the river. If the dam has given way – (he goes to the window.) Well, if it has, you can see for yourself that it means we can’t get out by the main road and we are already cut off from the south side. Look! (He points out of the window. Amy joins him. She gasps.)
 
Amy: Jim! The water is up around the garage! I thought it was just a pool in the garden, but it’s — it’s — Jim (soberly): The river. Yes, Ay, that’s old man river himself creeping up to your door. (Jim and Amy watch it a moment. Amy shudders.)

Amy: Oh, Jim, I’m scared!

Jim: (placing a hand on her shoulder) Steady, old pal! We’ve been through bad things before and come out safely. Remember the school fire? First thing, we must not let the others see how scared we are. Next, get all the things you can together here: water, food, blankets, coats, lights. I’m glad I served on the Junior Red Cross emergency squad during the war! It’s too bad you live in a bungalow instead of a two-storey house, but we can always climb into the attic and onto the roof.

Amy: (still staring out the window) How fast is the river raising, do you think, Jim?

Jim: I don’t know and it might stop before it reaches us. If only the rain would let up! We will signal for help from the roof. They will send a boat or something.
Explanation:
 
Jim was ready to help them. He said that was the reason he came there. Jim asked Amy to keep the Lantern prepared, and before he could say more, Betty said that she had a flashlight and some candles. Rose was still trying to call her mother. She was irritated because she was trying to reach the Main 3022 line, but she was not able to get through. Rose was scared and said that the line was dead. There was not even a buzzing sound on the line.
 
Jim understood everything he said maybe the line is down due to flood situation. He tried to prepare the girls for the worst. Jim told them to get everything whatever is needed. He asked Betty to take care of candles, lamps, lanterns, and flashlights. Next, he tells Rose to fill the tubs and buckets. Amy and Jim needed to look for some food, bedsheets, and coats. He even wants to take out the first-aid kit. Jim asked everyone to hurry up, so Rose and Betty went to take care of the chores. Jim tells Amy that it was a grave situation. He didn't want to scare Amy, but Amy's house is directly in line with the river. If the dam is underwater, then it means that they cannot go out on the main road and that they are cut off from the southern side already. Both Jim and Amy go near the window and see.
 
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Amy exclaimed to Jim that the water was up around the garage already. She said that she thought it was just another pool which forms due to incessant rains in the garden, but it's the river which has swelled up till here. She calls it the old man river which has come almost near the door. Both tremble a bit, and Amy told Jim that she was frightened. Jim consoled her by putting his hand around the shoulder. He said that they been through many incidents which had come and gone. He reminds her of even the school fire. He says the foremost thing is not to let others know that they are frightened.
 
He wanted Amy to get all the things like bedsheets, lanterns, coats, food, and water in one place. Jim was a part of the Junior Red Cross emergency squad during the war. So, he knows certain things. Jim said that it was a disappointment that Amy's house was a bungalow instead of a two-storied house. He said they all could climb to the roof if needed.

Amy asked Jim how fast is the river rising? Jim replies saying he had no idea and it might stop before entering the bungalow. He said that if the rain stops, he would climb the roof and call out for help. The rescuers might send a boat or something like that to rescue them.
 
Meanings of difficult words:
 
Numbers
Word
Meanings
1.
IrritationAnnoyance.
2.
Buzzing A low, continuous humming sound.
3.
SnappyCrisp.
4.
GarageA building for housing a motor vehicle.
5.
ShuddersShiver.
6.
Attic Loft.
Reference:
State Council of Educational Research and Training (2018). Term-1 English Standard-9. Old Man River By Dorothy Deming (Slightly adapted) (pp. 193-201). Published by the Tamil Nadu Textbook and Educational Services Corporation.