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

Sentence: 'a small doughnut held in a persons hand'. Find frequency of the letter 'n'
4

Sentence: 'hand holding a white calculator inside a store'. Find frequency of the letter 'o'
3

Sentence: 'a teddy bear in a hat on a city street'. Find frequency of the letter 'a'

5