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

Example Input: Sentence: 'a person with some scissors over a bowl'. Find frequency of the letter 's'
Example Output: 6

Example Input: Sentence: 'a man makes some cock tales at a desk'. Find frequency of the letter 'k'
Example Output: 3

Example Input: Sentence: 'luggage filled with a animal that was murdered for it's fur'. Find frequency of the letter 'n'
Example Output:
1