The radius of the bottom surface of a cylindrical oil barrel is 3 decimeters, if it is increased by 1 decimeter, the side area of the cylinder will increase by 12.56 square decimeters. What is the volume of this barrel in liters. (vessel wall thickness is ignored)
一个圆柱形油桶的底面半径是3分米，若把它增加1分米，圆柱的侧面积就增加12.56平方分米．这个油桶的容积是多少升．(容器壁厚忽略不计)
<gadget id="calculator">2 * 1</gadget>
<output>2</output>

<gadget id="calculator">3 ** 2</gadget>
<output>9</output>

<gadget id="calculator">3.14 * 9 * 2</gadget>
<output>56.52</output>

<result>56.52</result>