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

Ex Input:
Sentence: 'two men in black wet suits beside a white surfboard'. Find frequency of the letter 'e'

Ex Output:
5

Ex Input:
Sentence: 'a desk covered in notepads, a laptop and other devices'. Find frequency of the letter 'c'

Ex Output:
2

Ex Input:
Sentence: 'a small boy chewing on a blue and white toy'. Find frequency of the letter 'b'

Ex Output:
2