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

Ex Input:
Sentence: 'this marketplace has a lot of fresh fruit and vegetables'. Find frequency of the letter 'v'

Ex Output:
1

Ex Input:
Sentence: 'a girl sits on a surfboard and smiles'. Find frequency of the letter 'i'

Ex Output:
3

Ex Input:
Sentence: 'a person talking an a cell phone while drinking a cup of tea'. Find frequency of the letter 'l'

Ex Output:
4