In this task, you need to count the number of times the given letter appears in the given sentence.

[EX Q]: Sentence: 'a young boy wearing black and holding a skateboard on the sidewalk'. Find frequency of the letter 'n'
[EX A]: 5

[EX Q]: Sentence: 'a couple of boys in a field playing baseball'. Find frequency of the letter 'i'
[EX A]: 3

[EX Q]: Sentence: 'the room has a couch and tv in it'. Find frequency of the letter 'a'
[EX A]:
3