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

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

Example Input: Sentence: 'a man with a skateboard that is in the street'. Find frequency of the letter 'o'
Example Output: 1

Example Input: Sentence: 'person wearing helmet and riding motorcycle around a track'. Find frequency of the letter 'a'
Example Output:
5