TASK DEFINITION: In this task, you need to count the number of times the given letter appears in the given sentence.
PROBLEM: Sentence: 'small airplane in the process of taking off'. Find frequency of the letter 'e'

SOLUTION: 3

PROBLEM: Sentence: 'pedestrian in stripe clothing standing on street corner'. Find frequency of the letter 's'

SOLUTION: 4

PROBLEM: Sentence: 'a couple of dudes that are on a motorcycle'. Find frequency of the letter 'r'

SOLUTION:
2