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

Example Input: Sentence: 'a bike sitting parked next to a cart in front of some boxes'. Replace the letter 't' with 'x' in the sentence.
Example Output: a bike sixxing parked nexx xo a carx in fronx of some boxes

Example Input: Sentence: 'a man eats while holding himself up in a one-hand push up position'. Replace the letter 'i' with 'p' in the sentence.
Example Output: a man eats whple holdpng hpmself up pn a one-hand push up posptpon

Example Input: Sentence: 'an elephant in chains converses with a smaller elephant who is not wearing chains'. Replace the letter 'i' with 'm' in the sentence.
Example Output:
an elephant mn chamns converses wmth a smaller elephant who ms not wearmng chamns