Distance - please help! Is my teacher wrong?

Uhhh..both of you are very, very wrong. Perth, Australia and New York, NY are about 18,700 km apart! The site below shows how. They are very nearly on opposite ends of the earth, which is just under 40,000 km (it's 24,868 miles, which is 39,788.8 km), so I don't know how either of you got such low numbers.