After 3 meters of iron wire are used up, the ratio of what is used to what is left is 1:4. How long is this iron wire in meters?
一根铁丝用去3米后，用去的与剩下的比是1：4，这根铁丝长多少米？
<gadget id="calculator">1 + 4</gadget>
<output>5</output>

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

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

<result>15</result>