The upper base of a trapezoid is 20 meters, the height is 15 meters, and the lower base is twice the upper base. What is the area of the trapezoid in square meters?
一个梯形上底是20米，高是15米，下底是上底的2倍，这个梯形的面积是多少平方米
<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<gadget id="calculator">20 + 40</gadget>
<output>60</output>

<gadget id="calculator">15 / 2</gadget>
<output>15/2 = around 7.5</output>

<gadget id="calculator">60 * (15/2)</gadget>
<output>450</output>

<result>450</result>