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

Sentence: 'a birthday cake with a number one and three candle'. Find frequency of the letter 'w'
1

Sentence: 'a man serving himself pizza in a wooden booth'. Find frequency of the letter 'n'
4

Sentence: 'a group of people with racquets on a tennis court'. Find frequency of the letter 'r'

3