A trapezoid, the sum of the upper and lower bases is 20 decimeters, and the height is 60 centimeters, what is its area in square decimeters?
一个梯形，上底和下底的和是20分米，高是60厘米，它的面积是多少平方分米．
<gadget id="calculator">60 / 10</gadget>
<output>6</output>

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

<gadget id="calculator">20 * 3</gadget>
<output>60</output>

<result>60</result>