If the upper base of a trapezoid is extended by 6 cm, it becomes a parallelogram, and its area increases by 12 square centimeters than the original one. Knowing that the lower base of the original trapezoid is 15 cm long, what is the area of the original trapezoid?
一个梯形的上底延长6厘米，就成了一个平行四边形，面积比原来增加了12平方厘米已知原来梯形的下底长15厘米，求原来梯形的面积？
<gadget id="calculator">15 - 6</gadget>
<output>9</output>

<gadget id="calculator">9 + 15</gadget>
<output>24</output>

<gadget id="calculator">2 / 6</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">12 * (1/3)</gadget>
<output>4</output>

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

<gadget id="calculator">24 * 2</gadget>
<output>48</output>

<result>48</result>