A cylinder and a cone have the same base and height, if the sum of their volumes is 30 cubic decimeters, what is the difference between their volumes in cubic decimeters?
一个圆柱和一个圆锥等底等高，如果它们的体积之和是30立方分米，那么它们的体积之差是多少立方分米．
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">30 * (3/4)</gadget>
<output>45/2 = around 22.5</output>

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

<gadget id="calculator">30 * (1/4)</gadget>
<output>15/2 = around 7.5</output>

<gadget id="calculator">(45/2) - (15/2)</gadget>
<output>15</output>

<result>15</result>