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

Sentence: 'a couple of people are sitting at a table'. Find frequency of the letter 'e'
5

Sentence: 'a police officer who is riding on a horse'. Find frequency of the letter 'p'
1

Sentence: 'man standing on opposite side of tennis court holding racket'. Find frequency of the letter 'd'

3