TASK DEFINITION: In this task, you need to count the number of times the given letter appears in the given sentence.
PROBLEM: Sentence: 'a couple of people are sitting at a table'. Find frequency of the letter 'e'

SOLUTION: 5

PROBLEM: Sentence: 'a passenger bus that is driving down the street'. Find frequency of the letter 'r'

SOLUTION: 3

PROBLEM: Sentence: 'a green and yellow truck is driving on the road'. Find frequency of the letter 'o'

SOLUTION:
3