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 man riding his skateboard down low as he turns'. Find frequency of the letter 'g'
[A]: 1


[Q]: Sentence: 'the woman smiles while skiing near a couple of trees'. Find frequency of the letter 'a'
[A]:
3