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

Input: Consider Input: Sentence: 'a couple of people are sitting at a table'. Find frequency of the letter 'e'

Output: 5

Input: Consider Input: Sentence: 'a notebook and pen are left on a park bench'. Find frequency of the letter 'e'

Output: 5

Input: Consider Input: Sentence: 'a computer and sound equipment on a desk'. Find frequency of the letter 'm'
Output: 2