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: 'three woman are having a discussion in the kitchen'. Find frequency of the letter 'n'
5

Sentence: 'this is a desk with a computer on it'. Find frequency of the letter 's'

3

