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

Sentence: 'a man is water skiing on a river'. Find frequency of the letter 'r'
3

Sentence: 'pedestrian in stripe clothing standing on street corner'. Find frequency of the letter 's'
4

Sentence: 'there is a stop sign along with a 3 way sign on the same pole'. Find frequency of the letter 'h'

3