For a trapezoid, if the upper base is increased by 4 cm, the lower base and height remain unchanged, its area increases by 12 cm2; if the height is increased by 4 cm, the upper and lower bases remain unchanged, and the area increases by 16 cm2. What is the area of this trapezoid in square centimeters?
一个梯形，如果上底增加4厘米，下底和高都不变，它的面积增加12平方厘米，如果高增加4厘米，上、下底都不变，面积增加16平方厘米．这个梯形的面积是多少平方厘米？
<gadget id="calculator">16 / 4</gadget>
<output>4</output>

<gadget id="calculator">2 * 4</gadget>
<output>8</output>

<gadget id="calculator">12 / 4</gadget>
<output>3</output>

<gadget id="calculator">2 * 3</gadget>
<output>6</output>

<gadget id="calculator">6 / 2</gadget>
<output>3</output>

<gadget id="calculator">8 * 3</gadget>
<output>24</output>

<result>24</result>