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: 'three people are gathered around sitting on a park bench'. Find frequency of the letter 'g'
2

Sentence: 'a young woman holding a gun on a stove top oven sitting in a field'. Find frequency of the letter 'n'

8