The Characteristic Curve

Unfortunately your guess was wrong.
If you have calculated then certainly you have identified the power of the light bulb as 3 W at a voltage of 6 V. If a voltage of 9 V is used, the resulting power is 4,5 W.
The higher the voltage and the amperage that are used for the light bulb, the higher is the power of the light bulb.

You have now find out the effects of amperage and voltage on the power of a light bulb with the help of a U-I-diagram. You are very close the the solution of the brain-teaser!