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: 'pedestrians pass by a stop sign, some holding surfboards'. Find frequency of the letter 'n'
3

Sentence: 'two police motorcycles lead a motorcade or parade'. Find frequency of the letter 'c'
4