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

Ex Input:
Sentence: 'the bathroom is in need of remodel'. Find frequency of the letter 'e'

Ex Output:
5

Ex Input:
Sentence: 'a person riding a surfboard in the middle of a wave'. Find frequency of the letter 'o'

Ex Output:
3

Ex Input:
Sentence: 'a small doughnut held in a persons hand'. Find frequency of the letter 'n'

Ex Output:
4