A pot can only hold 2 cakes at a time. It takes 2 minutes to fry one side, and both sides must be fried. How many minutes does it take to cook 9 cakes at least.
一只锅，每次只能放2张饼．煎熟一面要2分钟，两面都要煎，煎熟9张饼最少要用多少分钟．
<gadget id="calculator">4 * 3</gadget>
<output>12</output>

<gadget id="calculator">2 * 3</gadget>
<output>6</output>

<gadget id="calculator">12 + 6</gadget>
<output>18</output>

<result>18</result>