square log is 15 decimeters long. When it is cut into four pieces, the surface area increases by 12 square decimeters. What is the volume of this square log in cubic decimeters?
一根方木长15分米，把它截成四段后，表面积增加了12平方分米，这根方木的体积是多少立方分米．
<gadget id="calculator">12 / 6</gadget>
<output>2</output>

<gadget id="calculator">2 * 15</gadget>
<output>30</output>

<result>30</result>