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

Example Input: Sentence: 'a half eaten doughnut in a persons hand'. Find frequency of the letter 'h'
Example Output: 3

Example Input: Sentence: 'city two way street with cars lined up on both sides'. Find frequency of the letter 'h'
Example Output: 2

Example Input: Sentence: 'two boxes covered with random photos of women'. Find frequency of the letter 'b'
Example Output:
1