copper wire is 21 cm long, and an aluminum wire is 16 cm long. If the two metal wires are cut off by how many centimeters, the remaining copper wire is exactly twice the length of the aluminum wire.
一根铜线长21厘米，一根铝线长16厘米，把这两根金属线都剪掉多少厘米，剩下的铜线恰好是铝线长度的2倍．
<gadget id="calculator">16 * 2</gadget>
<output>32</output>

<gadget id="calculator">32 - 21</gadget>
<output>11</output>

<gadget id="calculator">2 - 1</gadget>
<output>1</output>

<gadget id="calculator">11 / 1</gadget>
<output>11</output>

<result>11</result>