Read this and answer the question. If the question is unanswerable, say "unanswerable".

Norfolk Island Hospital is the only medical centre on the island. Medicare and the Pharmaceutical Benefits Scheme do not cover Norfolk Island. All visitors to Norfolk Island, including Australians, are recommended to purchase travel insurance. Although the hospital can perform minor surgery, serious medical conditions are not permitted to be treated on the island and patients are flown back to mainland Australia. Air charter transport can cost in the order of A$30,000. For serious emergencies, medical evacuations are provided by the Royal Australian Air Force. The island has one ambulance staffed by St John Ambulance Australia volunteers.

Where are Norfolk Island patients who need serious treatment flown to?
mainland Australia