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

Example Input: Sentence: 'a child sitting a table with a pizza in front of him'. Find frequency of the letter 'h'
Example Output: 3

Example Input: Sentence: 'guy leans on truck's hood while taking pics next to parked motorcycles'. Find frequency of the letter 's'
Example Output: 4

Example Input: Sentence: 'someone's desk has a computer, a keyboard, some pens, a journal, and a cell phone on it'. Find frequency of the letter 'o'
Example Output:
8