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

Example Input: Sentence: 'a woman is talking on her white phone'. Replace the letter 'w' with 'r' in the sentence.
Example Output: a roman is talking on her rhite phone

Example Input: Sentence: 'a yellow fire truck parked in a parking lot'. Replace the letter 'a' with 'y' in the sentence.
Example Output: y yellow fire truck pyrked in y pyrking lot

Example Input: Sentence: 'a man on a beach holding a surfboard'. Replace the letter 'b' with 'n' in the sentence.
Example Output:
a man on a neach holding a surfnoard