Three years ago, Rosie purchased an art piece for $4000. The same art piece will be three times as much in another three years. How much money will the art piece have increased by? Let's think first. Chain of thought:
If the art piece was bought at $4000, and its price in three years will be three times its buying price, it will be worth 3 * $4000 = $12000 in another three years. The price of the art piece will increase by $12000 - $4000 = $8000.
Therefore, the answer is 8000.