TASK DEFINITION: In this task, you need to count the number of times the given letter appears in the given sentence.
PROBLEM: Sentence: 'there is a zebra that is walking enar a car'. Find frequency of the letter 'r'

SOLUTION: 4

PROBLEM: Sentence: 'a young elephant is touching a bigger elephant with its trunk'. Find frequency of the letter 'i'

SOLUTION: 5

PROBLEM: Sentence: 'an old world war ii plan has been refurbished and modernized'. Find frequency of the letter 'n'

SOLUTION:
5