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

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

Example Input: Sentence: 'a variety of a different type of vegetables'. Find frequency of the letter 't'
Example Output: 4

Example Input: Sentence: 'the man is hitting the baseball during the game'. Find frequency of the letter 'h'
Example Output:
4