If the sum of the volumes of a cylinder and a cone with the same base and height is 20 cubic centimeters, what is the volume of the cylinder in cubic centimetres?
等底等高的圆柱和圆锥体积之和是20立方厘米，那么圆柱的体积是多少立方厘米．
<gadget id="calculator">1 + 3</gadget>
<output>4</output>

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

<gadget id="calculator">20 * (3/4)</gadget>
<output>15</output>

<result>15</result>