If the lengths of two adjacent sides of a parallelogram are 5 cm and 4 cm respectively, and the distance between one set of opposite sides is 4.5 cm, what is the area of the parallelogram in square centimeters?
一个平行四边形相邻两边的长度分别是5厘米和4厘米，其中一组对边之间的距离是4.5厘米，则这个平行四边形的面积是多少平方厘米．
<gadget id="calculator">4 * 4.5</gadget>
<output>18</output>

<result>18</result>