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

Example Input: Sentence: 'a young woman dressed in green and black operating a remote control'. Find frequency of the letter 'r'
Example Output: 5

Example Input: Sentence: 'the bathroom is in need of remodel'. Find frequency of the letter 'e'
Example Output: 5

Example Input: Sentence: 'a train pulling into a train station next to a housing structure'. Find frequency of the letter 'h'
Example Output:
1