Solution ratio: ((90-x)/14)=((90-2x)/10).
解比例：((90-x)/14)=((90-2x)/10)．
<gadget id="calculator">90 / 10</gadget>
<output>9</output>

<gadget id="calculator">90 / 14</gadget>
<output>45/7 = around 6.428571</output>

<gadget id="calculator">9 - (45/7)</gadget>
<output>18/7 = around 2.571429</output>

<gadget id="calculator">2 / 10</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 / 14</gadget>
<output>1/14 = around 0.071429</output>

<gadget id="calculator">(1/5) - (1/14)</gadget>
<output>9/70 = around 0.128571</output>

<gadget id="calculator">(18/7) / (9/70)</gadget>
<output>20</output>

<result>20</result>