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

Input: Consider Input: Sentence: 'two men with colorful ties are posing for a picture'. Find frequency of the letter 'r'

Output: 4

Input: Consider Input: Sentence: 'a train going over a bridge with some buildings in the background'. Find frequency of the letter 'd'

Output: 3

Input: Consider Input: Sentence: 'a man in a beanie is holding up a doughnut'. Find frequency of the letter 'h'
Output: 2