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

Ex Input:
Sentence: 'a couple walking down a sidewalk next to some graffiti'. Replace the letter 'a' with 'y' in the sentence.

Ex Output:
y couple wylking down y sidewylk next to some gryffiti

Ex Input:
Sentence: 'a man swinging at a tennis with a racquet on a court'. Replace the letter 't' with 'c' in the sentence.

Ex Output:
a man swinging ac a cennis wich a racquec on a courc

Ex Input:
Sentence: 'three blue utility sinks and two white regular sinks'. Replace the letter 'e' with 'o' in the sentence.

Ex Output:
throo bluo utility sinks and two whito rogular sinks