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

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: 'the ingredients are ready on the wooden table'. Find frequency of the letter 'w'

Ex Output:
1

Ex Input:
Sentence: 'a cat is sitting atop a pile of suitcases'. Find frequency of the letter 's'

Ex Output:
5