A small cone with a volume of 7 cubic decimeters is the largest possible cone cut from a cylinder. What is the volume of the cylinder in cubic decimeters?
体积是7立方分米的一个小圆锥是由一个圆柱削成的尽可能大的圆锥，圆柱体的积是多少立方分米．
<gadget id="calculator">7 * 3</gadget>
<output>21</output>

<result>21</result>