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

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

Ex Output:
a smaxx train is on the tracks by a house

Ex Input:
Sentence: 'a skater looks ahead as he rides down a ramp'. Replace the letter 'n' with 'm' in the sentence.

Ex Output:
a skater looks ahead as he rides dowm a ramp

Ex Input:
Sentence: 'a full-size fighter plane hanging in the air inside a building'. Replace the letter 't' with 'x' in the sentence.

Ex Output:
a full-size fighxer plane hanging in xhe air inside a building