cone and a cylinder have the same height, and the ratio of their base areas is 4:1. The volume of the cylinder is 21 cubic decimeters. What is the volume of the cone?
一个圆锥体和一个圆柱体的高相等，它们底面积的比是4：1，圆柱体的体积是21立方分米，圆锥的体积是多少立方分米．
<gadget id="calculator">4 / 3</gadget>
<output>4/3 = around 1.333333</output>

<gadget id="calculator">21 * (4/3)</gadget>
<output>28</output>

<result>28</result>