A sheep is tied to a vertex of a building by a 30-meter-long rope. The building is 20 meters long and 10 meters wide, surrounded by grass. How many square meters is the area of grass that can be eaten like this? (Pi is taken as 3)
一只羊被30米长的绳子拴在了建筑物的一个顶点上，建筑物长是20米，宽是10米，周围全是草地．样能吃到的草的面积是多少平方米？(圆周率取3)
<gadget id="calculator">30 ** 2</gadget>
<output>900</output>

<gadget id="calculator">360 - 90</gadget>
<output>270</output>

<gadget id="calculator">270 / 360</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">3 * 900 * (3/4)</gadget>
<output>2_025</output>

<gadget id="calculator">30 - 20</gadget>
<output>10</output>

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

<gadget id="calculator">90 / 360</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">3 * 100 * (1/4)</gadget>
<output>75</output>

<gadget id="calculator">30 - 10</gadget>
<output>20</output>

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

<gadget id="calculator">3 * 400 * (1/4)</gadget>
<output>300</output>

<gadget id="calculator">2_025 + 75 + 300</gadget>
<output>2_400</output>

<result>2_400</result>