A cylinder and a cone with the same base and height, the sum of their volumes is 84 cubic meters, what is the volume of the cone in cubic meters
等底等高的圆柱和圆锥，它们的体积之和是84立方米，则圆锥的体积是多少立方米
<gadget id="calculator">1 + 3</gadget>
<output>4</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">84 * (1/4)</gadget>
<output>21</output>

<result>21</result>