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

Sentence: 'the two dogs are playing in the pen together'. Find frequency of the letter 'o'
3

Sentence: 'there is a sandwich with a lot of meat cut in half'. Find frequency of the letter 'a'
5

Sentence: 'a bartender pouring multiple glasses of red wine'. Find frequency of the letter 'p'

2