The diameter of a circular roller skating rink is 30m, and the radius is increased by 5m after expansion. How many square meters is the area of the expansion?
一个圆形旱冰场的直径是30m，扩建后半径增加了5m，扩建的面积是多少平方米？
<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<gadget id="calculator">15 + 5</gadget>
<output>20</output>

<gadget id="calculator">20 ** 2</gadget>
<output>400</output>

<gadget id="calculator">3.14 * 400</gadget>
<output>1_256</output>

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

<gadget id="calculator">3.14 * 225</gadget>
<output>706.5</output>

<gadget id="calculator">1_256 - 706.5</gadget>
<output>549.5</output>

<result>549.5</result>