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

Input: Consider Input: Sentence: 'a double-decker bus covered in children's illustrations driving next to a van'. Find frequency of the letter 'a'

Output: 4

Input: Consider Input: Sentence: 'two laptop computers sitting on top of a white table'. Find frequency of the letter 'f'

Output: 1

Input: Consider Input: Sentence: 'a young boy holding food in his hands next to apple tree'. Find frequency of the letter 'o'
Output: 6