TASK DEFINITION: In this task, you need to count the number of times the given letter appears in the given sentence.
PROBLEM: Sentence: 'a train is sitting at a train station'. Find frequency of the letter 'r'

SOLUTION: 2

PROBLEM: Sentence: 'the receipts from a meal at a restaurant are for  a sandwich, chili, and apple'. Find frequency of the letter 'u'

SOLUTION: 1

PROBLEM: Sentence: 'a living room with a large book shelf filled with books'. Find frequency of the letter 'a'

SOLUTION:
3