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

Sentence: 'a man sitting inside a green military truck talking to someone'. Find frequency of the letter 'i'
7

Sentence: 'a person is riding in a cart pulled by a horse'. Find frequency of the letter 'a'
4

Sentence: 'a person on skies doing a flip in mid air'. Find frequency of the letter 'n'

4