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 passenger train that is going over a bridge'. Find frequency of the letter 't'
Example Output: 3

Example Input: Sentence: 'a photo of the past where two men walk down a road'. Find frequency of the letter 'h'
Example Output:
3