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: 'the sun goes down over a bike tied to a bench at the beach'. Find frequency of the letter 't'
5

Sentence: 'a van covered with graffiti parked on the sidewalk'. Find frequency of the letter 't'

3