If the radius and height of the base of the cylinder are doubled, the volume will be doubled.
如果圆柱的底面半径和高都扩大到原来的2倍，体积就扩大到原来的多少倍．
<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

<gadget id="calculator">4 * 2</gadget>
<output>8</output>

<result>8</result>