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

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

Sentence: 'a white plate topped with meat and greens'. Replace the letter 's' with 'b' in the sentence.
a white plate topped with meat and greenb

Sentence: 'a bunch of american flags are in the grass near some people'. Replace the letter 'n' with 'j' in the sentence.

a bujch of americaj flags are ij the grass jear some people