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

Example Input: Sentence: 'a back pack and lap top sit on the kitchen counter'. Replace the letter 't' with 'k' in the sentence.
Example Output: a back pack and lap kop sik on khe kikchen counker

Example Input: Sentence: 'a small train is on the tracks by a house'. Replace the letter 'l' with 'x' in the sentence.
Example Output: a smaxx train is on the tracks by a house

Example Input: Sentence: 'a kid with a backpack next to some water'. Replace the letter 'x' with 'b' in the sentence.
Example Output:
a kid with a backpack nebt to some water