TASK DEFINITION: In this task, you need to count the number of times the given letter appears in the given sentence.
PROBLEM: Sentence: 'a person riding a surfboard in the middle of a wave'. Find frequency of the letter 'o'

SOLUTION: 3

PROBLEM: Sentence: 'a group of men standing on the side of a boat'. Find frequency of the letter 'o'

SOLUTION: 5

PROBLEM: Sentence: 'a passenger train stopped at a platform for a train station'. Find frequency of the letter 'r'

SOLUTION:
5