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

Sentence: 'a person riding a surfboard in the middle of a wave'. Find frequency of the letter 'o'
3

Sentence: 'person wearing all white leaned up against a wall with a yellow sign'. Find frequency of the letter 'a'
8

Sentence: 'a street at night with trees and streetlights on'. Find frequency of the letter 't'

9