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

Sentence: 'a white toilet sitting next to a toilet paper roller'. Find frequency of the letter 'o'
4

Sentence: 'some people sitting on surfboards in the water'. Find frequency of the letter 't'
4

Sentence: 'a bow wearing a tie stands beside a door'. Find frequency of the letter 'e'

4