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

Example Input: Sentence: 'a person holding a wine glass in one hand and bread sticks in the other'. Find frequency of the letter 'd'
Example Output: 4

Example Input: Sentence: 'two metal  benches on an empty train platform'. Find frequency of the letter 'n'
Example Output: 4

Example Input: Sentence: 'town clocks affixed to a tall, brick building'. Find frequency of the letter 'r'
Example Output:
1