If you use a pan to cook pancakes, you can only fry up to 2 cakes at a time, and it takes 6 minutes to cook one cake (3 minutes on each side of the front and back), and how many minutes it takes to cook 7 cakes.
用一个平底锅煎饼，每次最多只能煎2个饼，煎一个饼需要6分钟(正反两面各煎3分钟)，煎7个饼需要多少分钟．
<gadget id="calculator">2 * 6</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>