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

Example Input: Sentence: 'a computer, keyboard, and mouse sitting on a desk'. Replace the letter 's' with 'c' in the sentence.
Example Output: a computer, keyboard, and mouce citting on a deck

Example Input: Sentence: 'a person with a cell phone standing next to a train'. Replace the letter 's' with 't' in the sentence.
Example Output: a perton with a cell phone ttanding next to a train

Example Input: Sentence: 'a man riding a motorcycle with another man hang off it's side'. Replace the letter 'm' with 'u' in the sentence.
Example Output:
a uan riding a uotorcycle with another uan hang off it's side