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

Sentence: 'a closet with a fan, luggage and various boxes'. Find frequency of the letter 'a'
6

Sentence: 'a double decker bus with a lot of people on board'. Find frequency of the letter 'l'
3

Sentence: 'a group of sheared and natural sheep in a green field'. Find frequency of the letter 'e'

7