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

Sentence: 'a group of people having dinner and drinking wine'. Find frequency of the letter 'r'
3

Sentence: 'a bed with a dog laying on it next to two laptop computers'. Find frequency of the letter 'n'
3

Sentence: 'broccoli, carrots, and cauliflower being stir fried in a black skilet'. Find frequency of the letter 'i'

7