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

Ex Input:
Sentence: 'a row of vintage cars in a grassy field'. Find frequency of the letter 'v'

Ex Output:
1

Ex Input:
Sentence: 'a red and white train passing a train station'. Find frequency of the letter 'a'

Ex Output:
7

Ex Input:
Sentence: 'a woman floating in a large blue pool of water'. Find frequency of the letter 'w'

Ex Output:
2