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

Example Input: Sentence: 'two little girls playing with a bat and a tennis ball'. Find frequency of the letter 'w'
Example Output: 2

Example Input: Sentence: 'different sets of luggage in a baggage claim area'. Find frequency of the letter 'r'
Example Output: 2

Example Input: Sentence: 'two people sitting on the floor eating pizza'. Find frequency of the letter 't'
Example Output:
5