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 pizza is in a box on a table outside'. Find frequency of the letter 'u'
1

Sentence: 'a grey hummingbird by fence and tree branches'. Find frequency of the letter 'y'

2