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

Sentence: 'a jet flying through the clear blue sky'. Find frequency of the letter 'g'
2

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

Sentence: 'a batter, catcher and umpire waiting for the pitch and a major league baseball game'. Find frequency of the letter 'c'
3