piece of iron wire is used up (3/5) for the first time, and 20% is used up for the second time, leaving 18 meters left. How long is this wire?
一根铁丝，第一次用去(3/5)，第二次用20%，还剩18米．这根铁丝原来有多长？
<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

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

<gadget id="calculator">(3/5) + (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 - (4/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">18 / (1/5)</gadget>
<output>90</output>

<result>90</result>