The height of a trapezoid is 12 cm and the lower base is three times the upper base. If its upper base is extended by 24 cm, it becomes a parallelogram. Find the area of this trapezoid.
一个梯形的高是12厘米，下底是上底的3倍．如果将它的上底延长24厘米就成为一个平行四边形．求这个梯形的面积．
<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">24 / 2</gadget>
<output>12</output>

<gadget id="calculator">12 * 3</gadget>
<output>36</output>

<gadget id="calculator">12 + 36</gadget>
<output>48</output>

<gadget id="calculator">24 / 2 / 2</gadget>
<output>6</output>

<gadget id="calculator">48 * 6</gadget>
<output>288</output>

<result>288</result>