A trapezoidal billboard is 3 meters long at the top, 5 meters long at the bottom, and 4 meters high. This billboard needs to be painted on both sides, and 0.4 kilograms of paint is used per square meter. How many kilograms of paint are needed to paint this billboard?
一个梯形广告牌上底长3米，下底长5米，高4米，这个广告牌的两面都要油漆，每平方米用油漆0.4千克，油漆这个广告牌共需要多少千克的油漆？
<gadget id="calculator">3 + 5</gadget>
<output>8</output>

<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">8 * 2 * 2 * 0.4</gadget>
<output>12.8</output>

<result>12.8</result>