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

Sentence: 'a couple of men standing inside of a liquor store'. Find frequency of the letter 'p'
1

Sentence: 'a man playing baseball on a television set'. Find frequency of the letter 'l'
4

Sentence: 'a male tennis player in a white shirt is playing tennis'. Find frequency of the letter 'e'

5