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 man sitting in front of a laptop computer next to a child'. Find frequency of the letter 'e'
2

Sentence: 'an elephant standing next to a pile of rocks'. Find frequency of the letter 'e'

4