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

Example Input: Sentence: 'a bunch of fruit sitting in a bowl, its overflowing'. Find frequency of the letter 't'
Example Output: 4

Example Input: Sentence: 'a man serving himself pizza in a wooden booth'. Find frequency of the letter 'n'
Example Output: 4

Example Input: Sentence: 'a plastic tray that has different foods inside of it'. Find frequency of the letter 't'
Example Output:
6