In the center of an open space with a length of 20 meters and a width of 15 meters, a fountain with a perimeter of 12.56 meters is built, and the remaining area is planted with grass. How many square meters is the area for planting grass?
在一个长20米，宽15米的空地中央，修一个周长是12.56米喷水池，剩下的面积种草，种草的面积是多少平方米？
<gadget id="calculator">20 * 15</gadget>
<output>300</output>

<gadget id="calculator">12.56 / 3.14 / 2</gadget>
<output>2</output>

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

<gadget id="calculator">3.14 * 4</gadget>
<output>12.56</output>

<gadget id="calculator">300 - 12.56</gadget>
<output>287.44</output>

<result>287.44</result>