In this task, you need to count the number of times the given letter appears in the given sentence.

Sentence: 'the receipts from a meal at a restaurant are for  a sandwich, chili, and apple'. Find frequency of the letter 'u'
1

Sentence: 'a woman cross country skiing in a competition'. Find frequency of the letter 's'
3

Sentence: 'a passenger bus that is driving down the street'. Find frequency of the letter 'r'

3