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 working on a small laptop on a wooden table'. Find frequency of the letter 'l'
Example Output: 4

Example Input: Sentence: 'two giraffes standing beside a building with tall doors'. Find frequency of the letter 'f'
Example Output:
2