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

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

Sentence: 'a softball player holding the bat on first base'. Find frequency of the letter 't'
4

Sentence: 'a person jumping up to catch a frisbee'. Find frequency of the letter 'a'

3