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

Sentence: 'a girl hitting a tennis ball on a court'. Find frequency of the letter 'l'
3

Sentence: 'a bed with a mattress that has nothing on it'. Find frequency of the letter 'a'
5

Sentence: 'a group of people having dinner and drinking wine'. Find frequency of the letter 'r'

3