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

Example Input: Sentence: 'a man standing in front of a statue near a metal pole'. Find frequency of the letter 'f'
Example Output: 2

Example Input: Sentence: 'a log in the water with three birds perched on it'. Find frequency of the letter 'r'
Example Output: 4

Example Input: Sentence: 'a woman sitting on the couch with her laptop'. Find frequency of the letter 'w'
Example Output:
2