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: 'a red train sitting at an empty station'. Replace the letter 'i' with 'h' in the sentence.
Example Output: a red trahn shtthng at an empty stathon

Example Input: Sentence: 'a tagged cow in a pasture of grass'. Replace the letter 's' with 'f' in the sentence.
Example Output:
a tagged cow in a pafture of graff