The lower base of a trapezoid is 4 times the length of the upper base. If the upper base is extended by 6 cm, the trapezoid becomes a parallelogram. What is the upper base of the trapezoid in cm?
一个梯形的下底是上底长度的4倍，如将上底延长6厘米，这个梯形就变成一个平行四边形，这个梯形上底是多少厘米．
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

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

<result>2</result>