The sum of the upper and lower bases of a trapezoid is 36dm, the height is 9dm, what is its area dm**2.
一个梯形上、下底之和为36dm，高为9dm，它的面积为多少dm**2．
<gadget id="calculator">18 / 2</gadget>
<output>9</output>

<gadget id="calculator">36 * 9</gadget>
<output>324</output>

<result>324</result>