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

Sentence: 'a sheep in a field in front of other sheep'. Find frequency of the letter 'f'
3

Sentence: 'a couple of people are sitting at a table'. Find frequency of the letter 'e'
5

Sentence: 'a large display of a hand holding a cell phone to tell the time'. Find frequency of the letter 'o'

4