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

Example Input: Sentence: 'a guy looking at a tennis ball with a goofy look'. Replace the letter 'a' with 'x' in the sentence.
Example Output: x guy looking xt x tennis bxll with x goofy look

Example Input: Sentence: 'an older man wearing a suit and tie'. Replace the letter 'i' with 't' in the sentence.
Example Output: an older man weartng a sutt and tte

Example Input: Sentence: 'a cat is wearing a pink wool hat'. Replace the letter 'c' with 'm' in the sentence.
Example Output:
a mat is wearing a pink wool hat