Mom wants to bake 5 cakes, only two cakes can be baked at a time, and both sides need to be baked, each side takes 3 minutes, at least how many minutes it will take to cook these 5 cakes.
妈妈要烙5张饼，每次只能烙两张，两面都要烙，每面3分钟，至少要多少分钟才能烙熟这5张饼．
<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>