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

Sentence: 'a flock of sheep grazing in a park'. Find frequency of the letter 'f'
2

Sentence: 'an orange cat sitting on the ground next to a  purse'. Find frequency of the letter 's'
2

Sentence: 'three baby elephants drinking water in a zoo environment'. Find frequency of the letter 'n'

7