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

Ex Input:
Sentence: 'man in a radio studio wearing a suit in front of a microphone'. Find frequency of the letter 't'

Ex Output:
3

Ex Input:
Sentence: 'two people are riding on canoes down a river'. Find frequency of the letter 'e'

Ex Output:
5

Ex Input:
Sentence: 'a skier skiing down a snowy pine-studded slope'. Find frequency of the letter 'n'

Ex Output:
4