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

Sentence: 'a stop sign next to houses with christmas lights'. Find frequency of the letter 's'
7

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

Sentence: 'a lady walking three cows through the town'. Find frequency of the letter 'e'

3