If the upper base of a trapezoid is increased by 2 cm, it becomes a square; if the upper base is reduced by 4 cm, it becomes a triangle. What is the area of the trapezoid in square centimeters?
一个梯形若上底增加2厘米，则成为一个正方形；若上底缩小4厘米，则成为一个三角形，这个梯形的面积是多少平方厘米
<gadget id="calculator">4 + 4 + 2</gadget>
<output>10</output>

<gadget id="calculator">4 + 2</gadget>
<output>6</output>

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

<gadget id="calculator">10 * 3</gadget>
<output>30</output>

<result>30</result>