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: 'flower in a vase full of water sitting on a stand '. Find frequency of the letter 'l'

Output: 3

Input: Consider Input: Sentence: 'a man that is on a surfboard in the ocean'. Find frequency of the letter 'd'
Output: 1