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

Sentence: 'a woman in a messy kitchen with a child'. Find frequency of the letter 'a'
4

Sentence: 'some people sitting on surfboards in the water'. Find frequency of the letter 't'
4

Sentence: 'a little cow with yellow ear tags standing around in some hay'. Find frequency of the letter 'd'
2