The upper base of a trapezoid is 5 cm, the lower base is 7 cm, and the height is 2.5 cm. What is the area of the trapezoid?
一个梯形的上底是5厘米，下底是7厘米，高是2.5厘米，这个梯形的面积是多少．
<gadget id="calculator">5 + 7</gadget>
<output>12</output>

<gadget id="calculator">2.5 / 2</gadget>
<output>1.25</output>

<gadget id="calculator">12 * 1.25</gadget>
<output>15</output>

<result>15</result>