The height of a trapezoid is 20 meters, and the sum of the upper and lower bases is 30 meters. What is the area of the trapezoid in square meters?
一个梯形的高是20米，上、下底的和是30米，梯形的面积是多少平方米．
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">30 * 10</gadget>
<output>300</output>

<result>300</result>