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

Sentence: 'a small white dog looking out a car window'. Find frequency of the letter 'l'
3

Sentence: 'a person with some scissors over a bowl'. Find frequency of the letter 's'
6

Sentence: 'a bunch of cows that are in the field'. Find frequency of the letter 'a'

3