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

Ex Input:
Sentence: 'children with scissors and construction paper in a school classroom'. Find frequency of the letter 'c'

Ex Output:
6

Ex Input:
Sentence: 'a man in a black shirt prepares to catch a frisbee'. Find frequency of the letter 'f'

Ex Output:
1

Ex Input:
Sentence: 'baseball players are playing baseball on a field'. Find frequency of the letter 'e'

Ex Output:
5