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

Example Input: Sentence: 'man in a radio studio wearing a suit in front of a microphone'. Find frequency of the letter 't'
Example Output: 3

Example Input: Sentence: 'children with scissors and construction paper in a school classroom'. Find frequency of the letter 'c'
Example Output: 6

Example Input: Sentence: 'a black and white picture of people lined up at a food truck'. Find frequency of the letter 'p'
Example Output:
4