It took 6 minutes to saw a piece of wood into 3 sections. How many minutes will it take to saw 7 sections at this speed?
一根木头锯了3段用了6分钟，照这样的速度锯成7段，还需多少分钟．
<gadget id="calculator">6 * 3</gadget>
<output>18</output>

<gadget id="calculator">18 - 6</gadget>
<output>12</output>

<result>12</result>