The upper base of a trapezoid is 4 cm. If the upper base is extended by 5 cm, the trapezoid becomes a parallelogram. What is the length of the bottom of the trapezoid in centimeters?
一个梯形的上底是4cm，如果将上底延长5cm，这个梯形就变成了一个平行四边形．这个梯形的下底长多少厘米．
<gadget id="calculator">4 + 5</gadget>
<output>9</output>

<result>9</result>