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

Sentence: 'a man skating down a stair rail in front of a bunch of people'. Find frequency of the letter 'o'
5

Sentence: 'a few men walking through a market place'. Find frequency of the letter 'f'
1

Sentence: 'a fat sheep standing in a grass field'. Find frequency of the letter 'd'
2