The sum of the upper and lower bases of a trapezoid is 28 cm, and the height is 15 cm. What is the area?
一个梯形上底和下底的和是28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">28 * (15/2)</gadget>
<output>210</output>

<result>210</result>