The area ratio of a trapezoid and a parallelogram is 3:2. Their heights are equal. The upper base of the trapezoid is 6 cm and the lower base is 9 cm. What is the base of the parallelogram in cm?
一个梯形和一个平行四边形面积比是3：2，它们的高相等，梯形的上底是6厘米，下底是9厘米，平行四边形的底是多少厘米．
<gadget id="calculator">6 / 2</gadget>
<output>3</output>

<gadget id="calculator">9 / 2</gadget>
<output>9/2 = around 4.5</output>

<gadget id="calculator">3 + (9/2)</gadget>
<output>15/2 = around 7.5</output>

<gadget id="calculator">3 / 2</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">(15/2) / (3/2)</gadget>
<output>5</output>

<result>5</result>