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

Example Input: Sentence: 'a tennis player after hitting a shot back to the other side of the court'. Find frequency of the letter 'n'
Example Output: 3

Example Input: Sentence: 'a variety of a different type of vegetables'. Find frequency of the letter 't'
Example Output: 4

Example Input: Sentence: 'someone is holding the muzzle of this black and tan dog'. Find frequency of the letter 'c'
Example Output:
1