The upper base of a trapezoid is 4 meters, 2 meters shorter than the lower base, and the height is as long as the upper base. What is the area of the trapezoid?
一个梯形的上底是4米，比下底短2米，高和上底一样长，这个梯形的面积是多少．
<gadget id="calculator">4 + 4 + 2</gadget>
<output>10</output>

<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">10 * 2</gadget>
<output>20</output>

<result>20</result>