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

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

Sentence: 'a man riding a white surfboard on a large wave'. Find frequency of the letter 'a'
7

Sentence: 'there is a clean counter top and sink'. Find frequency of the letter 'k'

1