The sum of the upper and lower bases of a trapezoid is 30 decimeters, which is three times the height. What is the area of the trapezoid in square decimeters?
一个梯形上、下底之和是30分米，是高的3倍，这个梯形的面积是多少平方分米．
<gadget id="calculator">30 / 3</gadget>
<output>10</output>

<gadget id="calculator">10 / 2</gadget>
<output>5</output>

<gadget id="calculator">30 * 5</gadget>
<output>150</output>

<result>150</result>