If the upper base of a trapezoid is 9 cm, and the lower base and height are both 15 cm, what is the area of the trapezoid in square centimeters?
一个梯形上底9厘米，下底和高都是15厘米，那么这个梯形的面积是多少平方厘米．
<gadget id="calculator">9 + 15</gadget>
<output>24</output>

<gadget id="calculator">15 / 2</gadget>
<output>15/2 = around 7.5</output>

<gadget id="calculator">24 * (15/2)</gadget>
<output>180</output>

<result>180</result>