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

Example Input: Sentence: 'a man is somewhat hard to be seen in the wave, on his board'. Replace the letter 's' with 'b' in the sentence.
Example Output: a man ib bomewhat hard to be been in the wave, on hib board

Example Input: Sentence: 'a couple sits on a bench in the countryside'. Replace the letter 'y' with 'k' in the sentence.
Example Output: a couple sits on a bench in the countrkside

Example Input: Sentence: 'three various colored suitcases next to a black and white guitar'. Replace the letter 'i' with 'f' in the sentence.
Example Output:
three varfous colored suftcases next to a black and whfte guftar