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

[EX Q]: Sentence: 'two computers and a laptop set up on a desk'. Find frequency of the letter 'r'
[EX A]: 1

[EX Q]: Sentence: 'a photo of a small boat on a shore'. Find frequency of the letter 'f'
[EX A]: 1

[EX Q]: Sentence: 'a man is riding on a street on his skate board'. Find frequency of the letter 'r'
[EX A]:
3