The lower base of a trapezoid is 12 decimeters. If one end of the upper base is extended by 4 decimeters, a parallelogram can be formed. At this time, the area will increase by 10 square decimeters. What is the area of the original trapezoid in square centimeters?
一个梯形的下底是12分米，把上底的一端延长4分米，可以成为一个平行四边形，这时面积将增加10平方分米．原来梯形的面积是多少平方分米．
<gadget id="calculator">12 - 4</gadget>
<output>8</output>

<gadget id="calculator">12 + 8</gadget>
<output>20</output>

<gadget id="calculator">2 / 4</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">10 * (1/2)</gadget>
<output>5</output>

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">20 * (5/2)</gadget>
<output>50</output>

<result>50</result>