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

Ex Input:
Sentence: 'the child is waving a small flag as she stands near two women'. Find frequency of the letter 'g'

Ex Output:
2

Ex Input:
Sentence: 'three men in military suits are sitting on a bench,'. Find frequency of the letter 'a'

Ex Output:
3

Ex Input:
Sentence: 'a woman sitting on the couch with her laptop'. Find frequency of the letter 'w'

Ex Output:
2