A trapezoid billboard has an upper base of 8 meters, a lower base of 12 meters, and a height of 6 meters. If you want to paint this billboard, it will cost 15 yuan per square meter, how much will it cost in total?
一个梯形广告牌，它的上底是8米，下底是12米，高是6米．如果要给这个广告牌涂上油漆，按每平方米花费15元来计算，共要花多少元？
<gadget id="calculator">12 + 8</gadget>
<output>20</output>

<gadget id="calculator">6 / 2</gadget>
<output>3</output>

<gadget id="calculator">20 * 3 * 15</gadget>
<output>900</output>

<result>900</result>