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: 'person wearing all white leaned up against a wall with a yellow sign'. Find frequency of the letter 'a'
[EX A]: 8

[EX Q]: Sentence: 'the girls are sitting down looking at their computers'. Find frequency of the letter 'd'
[EX A]:
1