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

Example Input: Sentence: 'a red train moves over snowy rail road tracks'. Replace the letter 'v' with 'w' in the sentence.
Example Output: a red train mowes ower snowy rail road tracks

Example Input: Sentence: 'a double decker bus stopped outside a station on a street'. Replace the letter 'c' with 'y' in the sentence.
Example Output: a double deyker bus stopped outside a station on a street

Example Input: Sentence: 'a truck drives in front a bus on a busy city street'. Replace the letter 's' with 'u' in the sentence.
Example Output:
a truck driveu in front a buu on a buuy city utreet