A pot can hold 2 cakes at a time, and both sides must be fried. It takes 3 minutes to fry one side, and how many minutes does it take to fry 7 cakes at least.
一只锅一次可放2块饼，两面都要煎，煎一面要3分钟，煎7块饼至少需要多少分钟．
<gadget id="calculator">3 * 2 * 2</gadget>
<output>12</output>

<gadget id="calculator">3 * 3</gadget>
<output>9</output>

<gadget id="calculator">12 + 9</gadget>
<output>21</output>

<result>21</result>