A pan can only put two cakes at a time. If one cake is baked on both sides and each side takes 3 minutes, then how many minutes is the minimum time needed to bake 5 cakes?
一个平底锅，每次只能放两张饼，如果一张饼两面都烙，每面需要3分钟，那么烙5张饼最少需要多少分钟．
<gadget id="calculator">2 * 3</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>