A trapezoid, the sum of the upper and lower bases is 60 cm, and the height is 15 cm, what is its area?
一个梯形，上底与下底的和是60厘米，高15厘米，它的面积是多少．
<gadget id="calculator">15 / 2</gadget>
<output>15/2 = around 7.5</output>

<gadget id="calculator">60 * (15/2)</gadget>
<output>450</output>

<result>450</result>