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

[EX Q]: Sentence: 'a man in a black shirt prepares to catch a frisbee'. Find frequency of the letter 'f'
[EX A]: 1

[EX Q]: Sentence: 'a player swings his bat at a baseball game'. Find frequency of the letter 'p'
[EX A]: 1

[EX Q]: Sentence: 'a group of people snowshoeing through a snowy trail'. Find frequency of the letter 'r'
[EX A]:
3