A bundle of wires, 35% is used up, exactly 42cm is used up, and the remaining 35% is used up, how many meters are left?
一捆电线，用去了35%，恰好用去42cm，再用去余下的35%，还剩多少米？
<gadget id="calculator">35 / 100</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">42 / (7/20)</gadget>
<output>120</output>

<gadget id="calculator">120 - 42</gadget>
<output>78</output>

<gadget id="calculator">78 * (7/20)</gadget>
<output>273/10 = around 27.3</output>

<gadget id="calculator">120 - 42 - (273/10)</gadget>
<output>507/10 = around 50.7</output>

<gadget id="calculator">(507/10) / 100</gadget>
<output>507/1_000 = around 0.507</output>

<result>507/1_000 = around 0.507</result>