There is a cuboid steel, 2 meters long, the cross-section is a square with a side length of 0.5 meters, and the steel weighs 7.8 kilograms per cubic meter. How many kilograms does this square steel weigh?
有一种长方体钢材，长2米，横截面是边长为0.5米的正方形，每立方米钢重7.8千克，这根方钢材重多少千克？
<gadget id="calculator">0.5 * 0.5 * 2 * 7.8</gadget>
<output>3.9</output>

<result>3.9</result>