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

Example Input: Sentence: 'a group of people standing around a table filled with assorted electronic devices'. Find frequency of the letter 'w'
Example Output: 1

Example Input: Sentence: 'a couple of people are sitting at a table'. Find frequency of the letter 'e'
Example Output: 5

Example Input: Sentence: 'sheep laying beneath a tree around farm equipment'. Find frequency of the letter 't'
Example Output:
3