A trapezoid, the sum of the upper and lower bases is 36 cm, the height is 15 cm, what is the area?
一个梯形，上底与下底的和是36厘米，高是15厘米，面积是多少．
<gadget id="calculator">15 / 2</gadget>
<output>15/2 = around 7.5</output>

<gadget id="calculator">36 * (15/2)</gadget>
<output>270</output>

<result>270</result>