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

[EX Q]: Sentence: 'a black cat laying down on a bed'. Find frequency of the letter 'y'
[EX A]: 1

[EX Q]: Sentence: 'a group of people seated in chairs together and facing the same direction, with one man holding a soccer ball in his hands'. Find frequency of the letter 'm'
[EX A]: 2

[EX Q]: Sentence: 'a desk with two monitors and a keyboard'. Find frequency of the letter 'd'
[EX A]:
3