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

Ex Input:
Sentence: 'a man with a large grey and black beard and glasses and a tie'. Find frequency of the letter 'e'

Ex Output:
5

Ex Input:
Sentence: 'an audience watches as a bird spreads its wings'. Find frequency of the letter 'd'

Ex Output:
3

Ex Input:
Sentence: 'an airplane is just about to complete it's full take off'. Find frequency of the letter 't'

Ex Output:
6