It costs 6 yuan to buy 3 bottles of mineral water, how much does it cost to buy 15 bottles of mineral water.
买3瓶矿泉水需要6元钱，买15瓶矿泉水需要多少元钱．
<gadget id="calculator">6 / 3</gadget>
<output>2</output>

<gadget id="calculator">2 * 15</gadget>
<output>30</output>

<result>30</result>