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

Sentence: 'a man playing baseball on a television set'. Find frequency of the letter 'l'
4

Sentence: 'a person on a surfboard in the surf of a wave'. Find frequency of the letter 's'
3

Sentence: 'a  large dog playing with a frying pan'. Find frequency of the letter 't'

1