How much cardboard is needed to make a pen holder with a bottom diameter of 12cm and a height of 15cm with cardboard?
用硬纸板做一个底面直径12cm，高15cm的笔筒，至少需要多少硬纸板？
<gadget id="calculator">3.14 * 12 * 15</gadget>
<output>565.2</output>

<gadget id="calculator">12 / 2</gadget>
<output>6</output>

<gadget id="calculator">6 ** 2</gadget>
<output>36</output>

<gadget id="calculator">3.14 * 36</gadget>
<output>113.04</output>

<gadget id="calculator">565.2 + 113.04</gadget>
<output>678.24</output>

<result>678.24</result>