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

Sentence: 'a microwave oven with a yellow note on the door'. Find frequency of the letter 'w'
3

Sentence: 'an image of a cautionary construction sign'. Find frequency of the letter 'a'
5

Sentence: 'a giraffe stands looking over a watering hole'. Find frequency of the letter 'n'

3