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

Example Input: Sentence: 'a small bird perched on some thin branches'. Replace the letter 'a' with 'f' in the sentence.
Example Output: f smfll bird perched on some thin brfnches

Example Input: Sentence: 'a red hydrant is sitting on the sidewalk in the city'. Replace the letter 'n' with 'r' in the sentence.
Example Output: a red hydrart is sittirg or the sidewalk ir the city

Example Input: Sentence: 'a man in a dress shirt, green tie and green plaid shorts'. Replace the letter 't' with 'b' in the sentence.
Example Output:
a man in a dress shirb, green bie and green plaid shorbs