A trapezoid, the height multiplied by the upper base is 36 square centimeters, and the height multiplied by the lower base is 72 square centimeters. What is the area of the trapezoid?
一个梯形，高乘以上底得36平方厘米，高乘以下底得72平方厘米，这个梯形的面积是多少．
<gadget id="calculator">36 + 72</gadget>
<output>108</output>

<gadget id="calculator">108 / 2</gadget>
<output>54</output>

<result>54</result>