The diameter of the bottom of a cylinder is 4 cm, if the height increases by 1 cm, how much does the surface area increase in square centimetres?
一个圆柱底面直径为4cm，如果高增加1cm，表面积增加多少平方厘米．
<gadget id="calculator">3.14 * 4 * 1</gadget>
<output>12.56</output>

<result>12.56</result>