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

Sentence: 'a piece of film shows two street signs crossing each other'. Find frequency of the letter 'f'
2

Sentence: 'a stop sign next to houses with christmas lights'. Find frequency of the letter 's'
7

Sentence: 'a los angeles school bus parked in a parking lot'. Find frequency of the letter 'a'

5