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

Sentence: 'group of snowboarders on a snowy trail overlooking a mountain'. Find frequency of the letter 'r'
5

Sentence: 'a line of people on motorcycles on the road'. Find frequency of the letter 'e'
5

Sentence: 'these horses are pulling a cart with two men on it'. Find frequency of the letter 'o'

3

