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

Sentence: 'a social occasion of people are uncovered before the open day'. Find frequency of the letter 'c'
4

Sentence: 'a man flying through the air on top of a skateboard'. Find frequency of the letter 'h'
3

Sentence: 'a person riding a snow board on a snowy surface'. Find frequency of the letter 'a'
5