A rope, 15% of its total length is used for the first time, and 25% of its total length is used for the second time, leaving 8.4 meters. How long is this rope originally?
一根绳子，第一次用去全长的15%，第二次用去全长的25%，还剩8.4米，这根绳子原来长多少米？
<gadget id="calculator">15 / 100</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (3/20) - (1/4)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">8.4 / (3/5)</gadget>
<output>14</output>

<result>14</result>