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

Example Input: Sentence: 'a zebra patterned set of hair brushes sitting on each other'. Replace the letter 'r' with 'a' in the sentence.
Example Output: a zebaa patteaned set of haia baushes sitting on each othea

Example Input: Sentence: 'a bathroom that has  a sink and a toilet'. Replace the letter 's' with 'a' in the sentence.
Example Output: a bathroom that haa  a aink and a toilet

Example Input: Sentence: 'a number of people board a passenger train'. Replace the letter 'a' with 'u' in the sentence.
Example Output:
u number of people bourd u pussenger truin