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

Example Input: Sentence: 'the man is holding a plastic sled with snow in it next to a child'. Find frequency of the letter 'g'
Example Output: 1

Example Input: Sentence: 'a room with a big screen television and a couch'. Find frequency of the letter 'h'
Example Output: 2

Example Input: Sentence: 'a black plate decorated with icing in a spider web pattern with a slice of cake in the middle'. Find frequency of the letter 'o'
Example Output:
2