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

Ex Input:
Sentence: 'a couple of buses parked on the side of the street'. Find frequency of the letter 'b'

Ex Output:
1

Ex Input:
Sentence: 'a young boy holding a piece of paper on top of a table'. Find frequency of the letter 'y'

Ex Output:
2

Ex Input:
Sentence: 'a duck flying above a large body of water'. Find frequency of the letter 'y'

Ex Output:
2