A piece of cuboid steel is 2 meters long and its cross-section is a square with side length 5 cm. Steel weighs 7.8 grams per cubic centimeter. How much does this square steel weigh?
一段长方体钢材，长2米，横截面是边长5厘米的正方形．每立方厘米钢重7.8克，这块方钢重多少？
<gadget id="calculator">7.8 / 1_000</gadget>
<output>0.0078</output>

<gadget id="calculator">5 * 5 * 2 * 100 * 0.0078</gadget>
<output>39</output>

<result>39</result>