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

[Q]: Sentence: 'two men are playing a video game as another sits watching'. Find frequency of the letter 'a'
[A]: 7

[Q]: Sentence: 'a person that is looking out his window'. Find frequency of the letter 'n'
[A]: 3

[Q]: Sentence: 'here's a cute souvenir from the urban experience'. Find frequency of the letter 'e'
[A]:
9