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

Example Input: Sentence: 'a group of three giraffes standing around a fence'. Replace the letter 't' with 'a' in the sentence.
Example Output: a group of ahree giraffes saanding around a fence

Example Input: Sentence: 'many street signs in front of a building while it is snowing'. Replace the letter 'r' with 'x' in the sentence.
Example Output: many stxeet signs in fxont of a building while it is snowing

Example Input: Sentence: 'the bowl of mashed potatoes has paprika sprinkled on the top'. Replace the letter 'e' with 'b' in the sentence.
Example Output:
thb bowl of mashbd potatobs has paprika sprinklbd on thb top