trapezoid is cut into a parallelogram and a triangle. The upper base of the trapezoid is 4.2 decimeters, the lower base is 6 decimeters, and the height is 5 decimeters. What is the area of the parallelogram cut?
一个梯形剪成一个平行四边形和一个三角形，梯形上底4.2分米，下底6分米，高5分米，剪得平行四边形面积是多少．
<gadget id="calculator">4.2 * 5</gadget>
<output>21</output>

<result>21</result>