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 piece of film shows two street signs crossing each other'. Find frequency of the letter 'f'
2

Sentence: 'a reflection of a table, chairs and umbrella from a pool'. Find frequency of the letter 'l'

5