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

Example Input: Sentence: 'the meal is served and ready to be eaten'. Find frequency of the letter 'e'
Example Output: 8

Example Input: Sentence: 'a player swings his bat at a baseball game'. Find frequency of the letter 'p'
Example Output: 1

Example Input: Sentence: 'a man is choosing food that hew wants to eat'. Find frequency of the letter 'd'
Example Output:
1