Stars A and B are exactly the same in their size. The temperature of Star A is 6,000 K while Star B is 12,000K. How do their luminosities compare?

1. Star A is twice as bright as Star B.
   
2. Star B is twice as bright as Star A.
   
3. Star A is 4 times as bright as Star B.
   
4. Star B is 4 times as bright as Star A.
   
5. Star A is 16 times as bright as Star B.
   
6. Star B is 16 times as bright as Star A.