TASK DEFINITION: In this task, you need to count the number of times the given letter appears in the given sentence.
PROBLEM: Sentence: 'a group of three dogs laying on a kitchen floor'. Find frequency of the letter 'r'

SOLUTION: 3

PROBLEM: Sentence: 'a red and white train passing a train station'. Find frequency of the letter 'a'

SOLUTION: 7

PROBLEM: Sentence: 'a group of buses that are sitting in the street'. Find frequency of the letter 'n'

SOLUTION:
2