The lower base of the trapezoid is 6 decimeters, the upper base is 9 decimeters, and the height is 2 decimeters. What is its area in square decimeters?
梯形的下底6分米，上底9分米，高2分米，它的面积多少平方分米．
<gadget id="calculator">6 + 9</gadget>
<output>15</output>

<gadget id="calculator">2 / 2</gadget>
<output>1</output>

<gadget id="calculator">15 * 1</gadget>
<output>15</output>

<result>15</result>