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

Sentence: 'apples, pears, and oranges are piled up for sale'. Find frequency of the letter 'a'
6

Sentence: 'a group of three dogs laying on a kitchen floor'. Find frequency of the letter 'r'
3

Sentence: 'a person in a hate is preparing to hit a ball with a green bat'. Find frequency of the letter 't'

5