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

Example Input: Sentence: 'an old rusty car sits outside of an old building'. Replace the letter 'o' with 'r' in the sentence.
Example Output: an rld rusty car sits rutside rf an rld building

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 group of people riding a wave on top of  surfboards'. Replace the letter 'g' with 'w' in the sentence.
Example Output:
a wroup of people ridinw a wave on top of  surfboards