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

Input: Consider Input: Sentence: 'a group of giraffes walk together by a hill'. Find frequency of the letter 'b'

Output: 1

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

Output: 1

Input: Consider Input: Sentence: 'a large brown dog sitting in the back seat of a car'. Find frequency of the letter 'a'
Output: 6