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

Sentence: 'there is a person standing on a blue towel'. Find frequency of the letter 'n'
4

Sentence: 'a parking meter painted green with a sign that describes it as not a parking meter'. Find frequency of the letter 's'
4

Sentence: 'a man is catching a frisbee in the air'. Find frequency of the letter 'a'

5