TASK DEFINITION: In this task, you need to count the number of times the given letter appears in the given sentence.
PROBLEM: Sentence: 'this yellow fire hydrant sits in a grass field'. Find frequency of the letter 'i'

SOLUTION: 5

PROBLEM: Sentence: 'a man on a skateboard going down a ramp while people are watching'. Find frequency of the letter 'w'

SOLUTION: 3

PROBLEM: Sentence: 'a pedestrian crossing sign is mounted to a pole'. Find frequency of the letter 'n'

SOLUTION:
4