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

Example Input: Sentence: 'a person holding a green cell phone in a classroom with many desks'. Replace the letter 'k' with 'w' in the sentence.
Example Output: a person holding a green cell phone in a classroom with many desws

Example Input: Sentence: 'giraffe standing on a pile of rocks reaching up to a branch with its mouth'. Replace the letter 'g' with 'n' in the sentence.
Example Output: niraffe standinn on a pile of rocks reachinn up to a branch with its mouth

Example Input: Sentence: 'a big table that has some people around it'. Replace the letter 'r' with 'y' in the sentence.
Example Output:
a big table that has some people ayound it