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

Example Input: Sentence: 'a person holding a wine glass in one hand and bread sticks in the other'. Find frequency of the letter 'd'
Example Output: 4

Example Input: Sentence: 'two bears swim in a blue pool of water'. Find frequency of the letter 'o'
Example Output: 4

Example Input: Sentence: 'assortment of vegetables with rice and meat on plate'. Find frequency of the letter 'r'
Example Output:
2