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

Sentence: 'a picture of two computers on a table'. Find frequency of the letter 'r'
2

Sentence: 'a boy catching a frisbee while standing ins bunch of leaves'. Find frequency of the letter 'a'
5

Sentence: 'some boys are sitting and playing a game on the wii'. Find frequency of the letter 'e'

4