The diameter of a circular roller skating rink is 30 meters, and the radius increases by 5 meters after expansion. How many square meters has the area of the roller skating rink increased after the expansion?
一个圆形旱冰场的直径是30米，扩建后半径增加了5米．扩建后旱冰场的面积增加了多少平方米？
<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">15 ** 2</gadget>
<output>225</output>

<gadget id="calculator">400 - 225</gadget>
<output>175</output>

<gadget id="calculator">3.14 * 175</gadget>
<output>549.5</output>

<result>549.5</result>