After cutting an 8 decimeter long cylindrical wood into two half cylinders along the diameter of the bottom surface, the sum of the surface area increases by 80 square decimeters. What is the volume of this wood in cubic decimeters?
把一根8分米长的圆柱形木料沿底面直径切成两个半圆柱后，表面积之和增加了80平方分米，这根木料的体积是多少立方分米．
<gadget id="calculator">80 / 2 / 8</gadget>
<output>5</output>

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">(5/2) ** 2</gadget>
<output>25/4 = around 6.25</output>

<gadget id="calculator">3.14 * (25/4) * 8</gadget>
<output>157</output>

<result>157</result>