trapezoid has an upper base of 30 meters, a lower base of 50 meters, and a height of 40 meters. What is the area of the trapezoid in square meters?
一个梯形上底30米，下底50米，高40米，这个梯形的面积是多少平方米？
<gadget id="calculator">30 + 50</gadget>
<output>80</output>

<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<gadget id="calculator">80 * 20</gadget>
<output>1_600</output>

<result>1_600</result>