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

Example Input: Sentence: 'a man sitting in a chair with a laptop in his lap'. Replace the letter 'p' with 'v' in the sentence.
Example Output: a man sitting in a chair with a lavtov in his lav

Example Input: Sentence: 'a dog laying in front of a horses stall with the horse peeking over the half door'. Replace the letter 'a' with 'b' in the sentence.
Example Output: b dog lbying in front of b horses stbll with the horse peeking over the hblf door

Example Input: Sentence: 'a walled garden has a bench and a fountain'. Replace the letter 'u' with 'y' in the sentence.
Example Output:
a walled garden has a bench and a foyntain