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

Example Input: Sentence: 'a man with a large grey and black beard and glasses and a tie'. Find frequency of the letter 'e'
Example Output: 5

Example Input: Sentence: 'a man in his car eating a donut'. Find frequency of the letter 'm'
Example Output: 1

Example Input: Sentence: 'a man in striped shirt swinging a baseball bat'. Find frequency of the letter 'e'
Example Output:
2