If the height of a cylinder of wood is reduced by 2 decimeters, the surface area will be reduced by 6.28 square decimeters. What is the volume of the reduced part?
一个圆柱体木料，如果把高减少2分米，表面积就减少6.28平方分米，求减少部分的体积是多少？
<gadget id="calculator">6.28 / 2 / 3.14 / 2</gadget>
<output>0.5</output>

<gadget id="calculator">0.5 ** 2</gadget>
<output>0.25</output>

<gadget id="calculator">3.14 * 0.25 * 2</gadget>
<output>1.57</output>

<result>1.57</result>