The height of a trapezoid is 12.3 cm, and the sum of the upper and lower bases is 9 cm. What is its area?
一个梯形，高是12.3厘米，上底与下底的和是9厘米，它的面积是多少．
<gadget id="calculator">12.3 / 2</gadget>
<output>6.15</output>

<gadget id="calculator">9 * 6.15</gadget>
<output>55.35</output>

<result>55.35</result>