A cylindrical steel is 2 meters long. If it is sawed into two pieces, the surface area will increase by 6.28 square decimeters compared to the original one. Find the mass of this 2-meter long steel. (7.8 kg per cubic decimeter of steel)
一根圆柱形钢材长2米，如果把它锯成两段，表面积比原来增加6.28平方分米，求这根2米长钢材的质量．(每立方分米钢重7.8千克)
<gadget id="calculator">6.28 / 2</gadget>
<output>3.14</output>

<gadget id="calculator">2 * 10</gadget>
<output>20</output>

<gadget id="calculator">3.14 * 20 * 7.8</gadget>
<output>489.84</output>

<result>489.84</result>