Question

I want a hot dog and an hamburger.
1. It's $6, isn't it?
2. They are $6, aren't they?

Which one is correct? Are both OK? Then what is the meaning of 'it' in #1?

Answer 1

1. The "it" would refer to the price.(singular)

2. The "they" would refer to the foods.
(plural)

So, both are ok.

Answer 2

A minor correction --

I want a hot dog and A hamburger.

We in the U.S. pronounce the "h" in hamburger, so we'd use "a" not "an" before this word.