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

Sentence: 'three men are in a kitchen cooking and cutting through a dish'. Find frequency of the letter 'a'
4

Sentence: 'a dog has found a rather large stick for playing fetch'. Find frequency of the letter 't'
3

Sentence: 'a black cow is walking through the streets of a town'. Find frequency of the letter 'e'

3