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

Ex Input:
Sentence: 'a fluffy white car looking in a mirror'. Find frequency of the letter 'k'

Ex Output:
1

Ex Input:
Sentence: 'a boy that is sitting at a table with pizza'. Find frequency of the letter 's'

Ex Output:
2

Ex Input:
Sentence: 'that looks like it could be a very delicious meal'. Find frequency of the letter 'c'

Ex Output:
2