A wire, if 40% of it is used, there are 12 meters left. If 70% of it is used, how much is left.
一根电线，如果用去它的40%，则剩下12米．如果用去它的70%，则剩下多少下．
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">12 / (3/5)</gadget>
<output>20</output>

<gadget id="calculator">70 / 100</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">20 * (7/10)</gadget>
<output>14</output>

<gadget id="calculator">20 - 14</gadget>
<output>6</output>

<result>6</result>