TASK DEFINITION: In this task, you need to count the number of times the given letter appears in the given sentence.
PROBLEM: Sentence: 'a red and white train passing a train station'. Find frequency of the letter 'a'

SOLUTION: 7

PROBLEM: Sentence: 'many white birds flying above a river that flows in front of a forest'. Find frequency of the letter 'a'

SOLUTION: 5

PROBLEM: Sentence: 'long slices of banana sit on a white plate'. Find frequency of the letter 'i'

SOLUTION:
3