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

Ex Input:
Sentence: 'a metallic stove top oven inside of a wooden kitchen'. Find frequency of the letter 'v'

Ex Output:
2

Ex Input:
Sentence: 'an old boat on a beach near a large body of water'. Find frequency of the letter 'a'

Ex Output:
8

Ex Input:
Sentence: 'a baseball player is up to bat at a game'. Find frequency of the letter 'r'

Ex Output:
1