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

Example Input: Sentence: 'there is a woman holding a tennis racket'. Replace the letter 'l' with 's' in the sentence.
Example Output: there is a woman hosding a tennis racket

Example Input: Sentence: 'a boy riding his skate board on an obstacle course'. Replace the letter 'e' with 'b' in the sentence.
Example Output: a boy riding his skatb board on an obstaclb coursb

Example Input: Sentence: 'a clock tower with roman numerals and a sun dial'. Replace the letter 'i' with 'a' in the sentence.
Example Output:
a clock tower wath roman numerals and a sun daal