TASK DEFINITION: In this task, you need to replace a letter in the sentence with another given letter.
PROBLEM: Sentence: 'a double decker bus stopped outside a station on a street'. Replace the letter 'c' with 'y' in the sentence.

SOLUTION: a double deyker bus stopped outside a station on a street

PROBLEM: Sentence: 'a mobile phone and a set of keys on a key chain'. Replace the letter 's' with 'j' in the sentence.

SOLUTION: a mobile phone and a jet of keyj on a key chain

PROBLEM: Sentence: 'a train yard with many passenger cars sitting in it'. Replace the letter 'i' with 'j' in the sentence.

SOLUTION:
a trajn yard wjth many passenger cars sjttjng jn jt