Theory:

     ‘Sir Francis,’ said Mr. Fogg quietly, ‘we will, if you please, look about for some means of transport to Allahabad.’
 
     ‘Mr. Fogg, this is a delay greatly to your disadvantage.’
 
     ‘No, Sir Francis; it was foreseen.’
 
     ‘What! You knew that the way—‘
 
     ‘Not at all; but I knew that some obstacle or other would sooner or later arise on my route. Nothing, therefore, is lost.
 
     I have two days, which I have already gained, to sacrifice. A steamer leaves Calcutta for Hong Kong at noon, on the 25th. This is the 22nd, and we shall reach Calcutta in time.’
Explanation:
 
Mr. Fogg seemed to be very quiet and understanding. He kept himself calm and did not get angry at everyone or the worst situation. Though Mr. Fogg had a purpose of completing his journey on time, he did not feel worried about it. Instead, he planned to handle the situation in a better way. He politely requested the general, Mr. Francis, to look for other means of transport to cross the remaining fifty kilometres from Kholby to Calcutta.

Francis was worried about Mr. Fogg's delay referring to Fogg's challenge in eighty days. He was worried that this incident was an obstacle to his tour progression. He did not expect this delay, but Mr. Fogg consoled him by saying the hurdle was expected. General Francis was confused. He asked Mr. Fogg whether he already knew about the issue associated with the railway route. Mr. Fogg replied that he did not know that there was an incomplete railway issue, but he still thought about some hurdle on his way. As Fogg had guessed about it, he didn't worry about the problem; he felt nothing was lost due to the problem.

The thing is, a ship starts from Calcutta on 25th noon in another two days. So, Mr. Fogg had two days in his hand. If he could catch that Calcutta ship on 25th, he would be able to reach Hong Kong. So, crossing fifty miles from Kholby to Allahabad and then reaching Calcutta in two days seems to be a possible task for Mr. Fogg since the 22nd.
 
Meaning of difficult words:
 
S.No
Words
Meaning
1.
Transport
A system of moving people from one place to another or vehicles you travel in
2.
Delay
A period of time that makes you to wait due to a problem that makes your work late
3.
Disadvantage
Something that cause you problem or hinder your success
4.
Hurdle/obstacle  
A problem or difficulty that you have to deal with to gain success
5.
Console
To make someone feel comfortable if they are sad 
6.
ForeseenTo realise, know or guess something in advance
7.
SteamerA boat or ship driven by steam
Reference:
State Council of Educational Research and Training (2019). Term-3 English Standard-7. A Journey by Train by Jules Verne (pp. 79-85). Published by the Tamil Nadu Textbook and Educational Services Corporation.