A trapezoidal steel plate has an upper base of 8.4 decimeters, a lower base of 12.6 decimeters, and a height of 5 decimeters. The steel plate weighs 0.8 kilograms per square decimeter. How many kilograms does this steel plate weigh?
一块梯形的钢板，上底8.4分米，下底12.6分米，高5分米，每平方分米钢板重0.8千克，这块钢板重多少千克？
<gadget id="calculator">8.4 + 12.6</gadget>
<output>21</output>

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">21 * (5/2) * 0.8</gadget>
<output>42</output>

<result>42</result>