The length of the upper base of a trapezoid is 5, and if the upper base is increased by 3, it becomes a square. What is the area of this trapezoid.
一个梯形的上底长5，如果上底增加3就变成了正方形．原来这个梯形的面积是多少．
<gadget id="calculator">5 + 3</gadget>
<output>8</output>

<gadget id="calculator">5 + 8</gadget>
<output>13</output>

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

<gadget id="calculator">13 * 4</gadget>
<output>52</output>

<result>52</result>