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

Example Input: Sentence: 'two indian women in colorful garb standing barefoot with two indian men'. Find frequency of the letter 'd'
Example Output: 3

Example Input: Sentence: 'three people are gathered around sitting on a park bench'. Find frequency of the letter 'g'
Example Output: 2

Example Input: Sentence: 'there is a small kitchen with black cabinets'. Find frequency of the letter 'h'
Example Output:
3