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

Example Input: Sentence: 'a train traveling through a dark tunnel next to green brush.'. Replace the letter 'r' with 'e' in the sentence.
Example Output: a teain teaveling theough a daek tunnel next to geeen beush.

Example Input: Sentence: 'commuter trains on tracks next to paved platform'. Replace the letter 'm' with 'w' in the sentence.
Example Output: cowwuter trains on tracks next to paved platforw

Example Input: Sentence: 'the child is throwing the frisbee through the hoop'. Replace the letter 't' with 'm' in the sentence.
Example Output:
mhe child is mhrowing mhe frisbee mhrough mhe hoop