TASK DEFINITION: In this task, you need to count the number of times the given letter appears in the given sentence.
PROBLEM: Sentence: 'a construction sign is displayed on a street'. Find frequency of the letter 'i'

SOLUTION: 4

PROBLEM: Sentence: 'two people are riding on canoes down a river'. Find frequency of the letter 'e'

SOLUTION: 5

PROBLEM: Sentence: 'a red double decker bus drives through a city,'. Find frequency of the letter 'o'

SOLUTION:
2