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

Sentence: 'men standing in the grass with a frisbee'. Find frequency of the letter 'a'
3

Sentence: 'a softball player holding the bat on first base'. Find frequency of the letter 't'
4

Sentence: 'a plate of food most likely for breakfast'. Find frequency of the letter 'o'

5