Theory:

     Suddenly she noticed the tongs in his hand. “Where did you find these tongs?”

     “I bought them.”
     “How much did you pay for them?”
     “Three paisas.”

     “You are a stupid child! It is almost noon and you haven’t had anything to eat or drink. Couldn’t you find anything better in the fair than this pair of iron tongs?”
 
     Hamid replied in an injured tone, “You burn your fingers on the iron pan so I bought them.” Granny was deeply moved by Hamid’s selflessness. She started crying. For the wretched woman, the pair of tongs was as precious as sacks of silver.
Explanation:
 
She saw the tongs in Hamid's hands and asked about it, the cost of it. He told her that he bought them for three paisas.
 
Grandmother was worried that Hamid had left long back. He did not eat or drink from that time and asked why he didn't buy anything to eat instead of tongs. Hamid said that he bought the tongs for her so that she would not burn her hands anymore while cooking.
 
Grandmother was too touched by his concern for her than with his own. For her, it was the most precious thing than a bags of silver.
  
Meanings of difficult words:
 
Numbers
Words
Meanings
1.
Deeply moved
Touched.
2.
Selflessness  
Concern more with the needs and wishes of others than with one's own.
Reference:
 
State Council of Educational Research and Training (2019). Term-1 English Standard-7. Eidgah -Story by Munshi Premchand, Translated and Adapted by Uma Raman  (pp. 01-08). Published by the Tamil Nadu Textbook and Educational Services Corporation.