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

Example Input: Sentence: 'a person with some scissors over a bowl'. Find frequency of the letter 's'
Example Output: 6

Example Input: Sentence: 'large grassy pasture filled with trees and a single horse'. Find frequency of the letter 'l'
Example Output: 4

Example Input: Sentence: 'a tilted view of a curve in a mountainous road'. Find frequency of the letter 'o'
Example Output:
4