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

Example Input: Sentence: 'a half eaten doughnut in a persons hand'. Find frequency of the letter 'h'
Example Output: 3

Example Input: Sentence: 'a boy swinging a bat while playing baseball'. Find frequency of the letter 'h'
Example Output: 1

Example Input: Sentence: 'a collection of light wood cabinets sit in a warehouse'. Find frequency of the letter 'w'
Example Output:
2