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

Ex Input:
Sentence: 'a fluffy white car looking in a mirror'. Find frequency of the letter 'k'

Ex Output:
1

Ex Input:
Sentence: 'a gray airplane with metal petals on the wings takes off from an airport'. Find frequency of the letter 'i'

Ex Output:
4

Ex Input:
Sentence: 'breakfast of boiled egg and other snacks with juice are on the table'. Find frequency of the letter 't'

Ex Output:
5