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

Sentence: 'a person on a surfboard in the surf of a wave'. Find frequency of the letter 's'
3

Sentence: 'a woman sitting in front of a giant slice of cheese pizza'. Find frequency of the letter 'e'
4

Sentence: 'a man and a woman are walking down the street with an umbrella over their heads'. Find frequency of the letter 'w'

4