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

Example Input: Sentence: 'the sun goes down over a bike tied to a bench at the beach'. Find frequency of the letter 't'
Example Output: 5

Example Input: Sentence: 'a tv in a glass mirror in the bathroom'. Find frequency of the letter 'h'
Example Output: 2

Example Input: Sentence: 'a young man standing and posing in a chicago cubs baseball uniform'. Find frequency of the letter 'a'
Example Output:
8