A circular road with a width of 5 meters is paved around a circular lawn with a diameter of 20 meters. Find the area of the circular road.
在一个直径20米的圆形草地周围铺一条宽5米的环形道路，求这条环形路的面积是多少．
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">10 + 5</gadget>
<output>15</output>

<gadget id="calculator">15 ** 2</gadget>
<output>225</output>

<gadget id="calculator">10 ** 2</gadget>
<output>100</output>

<gadget id="calculator">225 - 100</gadget>
<output>125</output>

<gadget id="calculator">3.14 * 125</gadget>
<output>392.5</output>

<result>392.5</result>