The height of a cylinder is 20 cm. If the height is reduced by 4 cm, the surface area is reduced by 125.6 cm2. Find the volume of the original cylinder.
一个圆柱体的高是20厘米，若高减少4厘米，则表面积减少125.6平方厘米，求原来圆柱体的体积．
<gadget id="calculator">125.6 / 4</gadget>
<output>31.4</output>

<gadget id="calculator">31.4 / 3.14 / 2</gadget>
<output>5</output>

<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<gadget id="calculator">3.14 * 25 * 20</gadget>
<output>1_570</output>

<result>1_570</result>