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

Sentence: 'a couple of men sitting next to each other under an umbrella'. Find frequency of the letter 'n'
5

Sentence: 'a jet that is flying in the sky with a banner behind it'. Find frequency of the letter 'r'
1

Sentence: 'two young women playing a game of tennis with two opponents'. Find frequency of the letter 't'

5