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

Ex Input:
Sentence: 'a jet flying through the clear blue sky'. Find frequency of the letter 'g'

Ex Output:
2

Ex Input:
Sentence: 'a woman in a messy kitchen with a child'. Find frequency of the letter 'a'

Ex Output:
4

Ex Input:
Sentence: 'a group of woman chasing a soccer ball'. Find frequency of the letter 'c'

Ex Output:
3