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

Example Input: Sentence: 'a giraffe and a zebra stare at each other'. Replace the letter 'g' with 'l' in the sentence.
Example Output: a liraffe and a zebra stare at each other

Example Input: Sentence: 'two zebras are snuggling at the zoo in their display area'. Replace the letter 'e' with 'z' in the sentence.
Example Output: two zzbras arz snuggling at thz zoo in thzir display arza

Example Input: Sentence: 'a private sized airplane that is on a runway'. Replace the letter 'r' with 'f' in the sentence.
Example Output:
a pfivate sized aifplane that is on a funway