There is a rectangular parallelepiped steel with a length of 5 meters, which is cut into 4 sections, and the surface area is increased by 120 square decimeters. If the steel weighs 7.8 kilograms per cubic decimeter, how many kilograms does this steel weigh?
有一根长5米的长方体钢材，把它横截成4段，表面积增加了120平方分米，如果每立方分米钢重7.8千克，这根钢材重多少千克？
<gadget id="calculator">120 / 6</gadget>
<output>20</output>

<gadget id="calculator">5 * 10</gadget>
<output>50</output>

<gadget id="calculator">20 * 50 * 7.8</gadget>
<output>7_800</output>

<result>7_800</result>