One pan can only put 2 cakes at a time, one cake needs to be baked on both sides, it takes 3 minutes to cook one side, and how many minutes is the minimum time to bake 5 cakes.
一个平底锅，每次只能放2张饼，一张饼要烙两面，把烙熟一面要3分钟，烙5张饼至少要多少分钟．
<gadget id="calculator">3 * 2</gadget>
<output>6</output>

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

<gadget id="calculator">6 + 9</gadget>
<output>15</output>

<result>15</result>