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

Example input: Sentence: 'group of motorcycle motorists trying to merge into traffic'. Replace the letter 'o' with 'n' in the sentence.
Example output: grnup nf mntnrcycle mntnrists trying tn merge intn traffic
Example explanation: The letter 'o' has been replaced in the letter 'n'.
Q: Sentence: 'this a classroom that has many desk and papers everywhere'. Replace the letter 's' with 'f' in the sentence.
A:
thif a claffroom that haf many defk and paperf everywhere