A right-angled trapezoidal vegetable field has a lower base of 40m, if the upper base is increased by 8m, the vegetable field becomes a square. What is the area of the original trapezoid?
一块直角梯形的菜地，它的下底是40m，如果上底增加8m，这块菜地就变成了正方形．原来梯形的面积是多少？
<gadget id="calculator">40 - 8</gadget>
<output>32</output>

<gadget id="calculator">32 + 40</gadget>
<output>72</output>

<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<gadget id="calculator">72 * 20</gadget>
<output>1_440</output>

<result>1_440</result>