There is a parallelogram billboard with a base of 2.8m and a height of 1.5m. To paint the front and back sides of the billboard, 0.45 kg of paint is used per square meter, how many kg of paint is used.
有一个平行四边形广告牌，底是2.8m，高是1.5m，要粉刷这个广告牌的正反两面，每平方米用油漆0.45千克，共用油漆多少千克．
<gadget id="calculator">2.8 * 1.5 * 2 * 0.45</gadget>
<output>3.78</output>

<result>3.78</result>