A robot model is sold as second-hand goods for 72 yuan, and it loses 20%. If the original price is 126 yuan, what percentage can it earn?
一个机器人模型，作为旧货处理72元卖出去，亏了20%，如果按原来的标价126元，可以赚百分之几？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">72 / (4/5)</gadget>
<output>90</output>

<gadget id="calculator">126 - 90</gadget>
<output>36</output>

<gadget id="calculator">36 / 90</gadget>
<output>2/5 = around 0.4</output>

<result>2/5 = around 0.4</result>