Two cakes can be baked in one pot at a time, and it takes 3 minutes to cook one side, and how many minutes is the minimum time to bake 7 cakes.
一个锅里每次能烙两张饼，烙熟一面要3分钟，烙7张饼最少要多少分钟．
<gadget id="calculator">2 * 2 * 3</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>