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

Example Input: Sentence: 'an older red airplane is going straight up'. Replace the letter 'h' with 'z' in the sentence.
Example Output: an older red airplane is going straigzt up

Example Input: Sentence: 'a bunch of animals that are runing in a field'. Replace the letter 'm' with 'j' in the sentence.
Example Output: a bunch of anijals that are runing in a field

Example Input: Sentence: 'a dog with a herd of cows on a hillside'. Replace the letter 'e' with 'c' in the sentence.
Example Output:
a dog with a hcrd of cows on a hillsidc