TASK DEFINITION: In this task, you need to count the number of times the given letter appears in the given sentence.
PROBLEM: Sentence: 'a double-decker bus covered in children's illustrations driving next to a van'. Find frequency of the letter 'a'

SOLUTION: 4

PROBLEM: Sentence: 'a double parking meter is decorated with a picture of a girl with wings on her feet'. Find frequency of the letter 'r'

SOLUTION: 6

PROBLEM: Sentence: 'a boy in a baseball uniform standing on the pitcher's rubber'. Find frequency of the letter 'a'

SOLUTION:
5