A trapezoid, the ratio of the length of the upper base to the lower base is 4:7, if the upper base is extended by 15 cm, it becomes a rectangle, and the area increases by 90 square centimeters, what is the area of the trapezoid in square centimeters?
一个梯形，上底与下底长度的比是4：7，如果把上底延长15厘米，就成了一个长方形，并且面积增加了90平方厘米，原来这个梯形的面积是多少平方厘米．
<gadget id="calculator">7 - 4</gadget>
<output>3</output>

<gadget id="calculator">15 / 3</gadget>
<output>5</output>

<gadget id="calculator">4 * 5</gadget>
<output>20</output>

<gadget id="calculator">5 * 7</gadget>
<output>35</output>

<gadget id="calculator">20 + 35</gadget>
<output>55</output>

<gadget id="calculator">2 / 15</gadget>
<output>2/15 = around 0.133333</output>

<gadget id="calculator">90 * (2/15)</gadget>
<output>12</output>

<gadget id="calculator">12 / 2</gadget>
<output>6</output>

<gadget id="calculator">55 * 6</gadget>
<output>330</output>

<result>330</result>