A triangle and a parallelogram have the same area and height. It is known that the base of the parallelogram is 9 decimeters. How many decimeters is the base of the triangle.
一个三角形和一个平行四边形的面积相等，高也相等，已知平行四边形的底是9分米，三角形的底是多少分米．
<gadget id="calculator">9 * 2</gadget>
<output>18</output>

<result>18</result>