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

Ex Input:
Sentence: 'man riding a skate board down the little board way'. Find frequency of the letter 'k'

Ex Output:
1

Ex Input:
Sentence: 'different sets of luggage in a baggage claim area'. Find frequency of the letter 'r'

Ex Output:
2

Ex Input:
Sentence: 'a serving plate with sandwich slices arranged around eggs'. Find frequency of the letter 'd'

Ex Output:
3