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

Example Input: Sentence: 'a man eats while holding himself up in a one-hand push up position'. Replace the letter 'i' with 'p' in the sentence.
Example Output: a man eats whple holdpng hpmself up pn a one-hand push up posptpon

Example Input: Sentence: 'a row of lawn chairs with umbrellas over them'. Replace the letter 'e' with 'x' in the sentence.
Example Output: a row of lawn chairs with umbrxllas ovxr thxm

Example Input: Sentence: 'a few planes flying in the air over a city'. Replace the letter 'h' with 'x' in the sentence.
Example Output:
a few planes flying in txe air over a city