You can only bake two cakes at a time, and it takes 4 minutes to bake one side, and how many minutes is the minimum time to bake 7 cakes.
每次只能烙两张饼，烙一面要4分钟，烙7个饼最少要多少分钟分钟．
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">4 * 2 * 2</gadget>
<output>16</output>

<gadget id="calculator">4 * 3</gadget>
<output>12</output>

<gadget id="calculator">16 + 12</gadget>
<output>28</output>

<result>28</result>