piece of iron wire, use up the full length (3/10) for the first time, use 3 meters more than the first time for the second time, use up 20% of the full length for the third time, just run out, this iron wire How many meters is the total length?
一根铁丝，第一次用去全长的(3/10)，第二次用去的比第一次多3米，第三次用去全长的20%，正好用完，这根铁丝全长多少米？
<gadget id="calculator">3 / 10</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (3/10) - (3/10) - (1/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">3 / (1/5)</gadget>
<output>15</output>

<result>15</result>