On a piece of rectangular land with a length of 10m and a width of 8m, build the largest circular fountain, what is the area of the remaining open space in square meters?
在一块长10m，宽8m的长方形土地上，修建一个最大的圆形喷水池，求剩余空地的面积是多少平方米？
<gadget id="calculator">10 * 8</gadget>
<output>80</output>

<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

<gadget id="calculator">3.14 * 16</gadget>
<output>50.24</output>

<gadget id="calculator">80 - 50.24</gadget>
<output>29.76</output>

<result>29.76</result>