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

Example Input: Sentence: 'salad and vegetables with me on top of plate'. Find frequency of the letter 'o'
Example Output: 3

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

Example Input: Sentence: 'two woman stand and text on their cellphones'. Find frequency of the letter 'p'
Example Output:
1