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

Sentence: 'three young children playing with a ball in front of a huge bridge'. Find frequency of the letter 'e'
5

Sentence: 'a cat sleeping near lots of pairs of shoes'. Find frequency of the letter 'r'
2

Sentence: 'a city bus is traveling down the street'. Find frequency of the letter 's'

3