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

Example Input: Sentence: 'three young people goofing around; one of the guys has a football, the girl has a teddy bear'. Find frequency of the letter 'd'
Example Output: 3

Example Input: Sentence: 'a toasted sub sandwich is next to a salad'. Find frequency of the letter 'a'
Example Output: 6

Example Input: Sentence: 'many people are scattered around a huge table of food'. Find frequency of the letter 'h'
Example Output:
1