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

Example Input: Sentence: 'slices of orange are arranged on a plate'. Find frequency of the letter 's'
Example Output: 2

Example Input: Sentence: 'man in a radio studio wearing a suit in front of a microphone'. Find frequency of the letter 't'
Example Output: 3

Example Input: Sentence: 'three large giraffes with one small standing next to a building'. Find frequency of the letter 'e'
Example Output:
6