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

Ex Input:
Sentence: 'a traffic signal by a wire filled with some birds'. Find frequency of the letter 'e'

Ex Output:
3

Ex Input:
Sentence: 'a airplane view of a big factory some people and cars'. Find frequency of the letter 'f'

Ex Output:
2

Ex Input:
Sentence: 'a woman standing on a street corner next to a traffic light'. Find frequency of the letter 't'

Ex Output:
7