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

[EX Q]: Sentence: 'a couple of buses parked on the side of the street'. Find frequency of the letter 'b'
[EX A]: 1

[EX Q]: Sentence: 'a blue tripocal bird is perched on a wooden fence'. Find frequency of the letter 'd'
[EX A]: 3

[EX Q]: Sentence: 'a couple of sheep walking through a field of tall grass'. Find frequency of the letter 's'
[EX A]:
3