There are two iron wires, the first one is 28 meters long, and the second one is 20 meters long. After the two iron wires are used for the same length, the remaining length of the first wire is three times that of the second one. The remaining length of the first iron wire is How much rice.
有两根铁丝，第一根长28米，第二根长20米，两根铁丝用去同样长一段后，第一根剩下的长度是第二根的3倍，第一根铁丝剩下多少米．
<gadget id="calculator">28 - 20</gadget>
<output>8</output>

<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<gadget id="calculator">4 * 3</gadget>
<output>12</output>

<result>12</result>