In this task, you need to replace a letter in the sentence with another given letter.

Example Input: Sentence: 'three young school girls waiting on a subway train platform'. Replace the letter 't' with 'o' in the sentence.
Example Output: ohree young school girls waioing on a subway orain plaoform

Example Input: Sentence: 'many people gathered on a sunny day flying kites'. Replace the letter 'e' with 'm' in the sentence.
Example Output: many pmoplm gathmrmd on a sunny day flying kitms

Example Input: Sentence: 'a group of people are on the water'. Replace the letter 'w' with 'q' in the sentence.
Example Output:
a group of people are on the qater