The sum of the upper and lower bases of a trapezoid is 12cm, and the height is 9cm. What is its area in cm**2.
一个梯形的上、下底的和是12cm，高是9cm，它的面积是多少cm**2．
<gadget id="calculator">9 / 2</gadget>
<output>9/2 = around 4.5</output>

<gadget id="calculator">12 * (9/2)</gadget>
<output>54</output>

<result>54</result>