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

Sentence: 'pedestrian in stripe clothing standing on street corner'. Find frequency of the letter 's'
4

Sentence: 'this is a sign in front of a large cathedral'. Find frequency of the letter 'a'
5

Sentence: 'an airborne snowboarder is captured mid-jump between two snow piles'. Find frequency of the letter 'e'

7