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

Example Input: Sentence: 'a couple of horses with carriages at a building'. Replace the letter 'u' with 'm' in the sentence.
Example Output: a comple of horses with carriages at a bmilding

Example Input: Sentence: 'a man eats food that is inside a banana peel'. Replace the letter 'n' with 'k' in the sentence.
Example Output: a mak eats food that is ikside a bakaka peel

Example Input: Sentence: 'a small dog wearing a bright red bow tie as a collar'. Replace the letter 'e' with 'f' in the sentence.
Example Output:
a small dog wfaring a bright rfd bow tif as a collar