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

Example Input: Sentence: 'two zebra stand near the wooden posts on a building'. Find frequency of the letter 't'
Example Output: 4

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

Example Input: Sentence: 'a man sneers while wearing a dark suit and tie'. Find frequency of the letter 'h'
Example Output:
1