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

[Q]: Sentence: 'a person is riding in a cart pulled by a horse'. Find frequency of the letter 'a'
[A]: 4


[Q]: Sentence: 'a fluffy white car looking in a mirror'. Find frequency of the letter 'k'
[A]: 1


[Q]: Sentence: 'a ham sandwich on a place with a green salad'. Find frequency of the letter 'a'
[A]:
8