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

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

Example Input: Sentence: 'the child is waving a small flag as she stands near two women'. Find frequency of the letter 'g'
Example Output: 2

Example Input: Sentence: 'a plastic animal on a stick in teh ground next to three stone sculpture'. Find frequency of the letter 'o'
Example Output:
4