Wang Qiang practiced brush writing and wrote 12 pages in 3 days. At this speed, how many days would it take him to finish 80 pages?
王强练习写毛笔字，3天写12页，照这样的速度，他写完80页要多少天．
<gadget id="calculator">12 / 3</gadget>
<output>4</output>

<gadget id="calculator">80 / 4</gadget>
<output>20</output>

<result>20</result>