Central Primary School has a circular flower bed with a diameter of 8 meters, and now it is going to build a circular green belt with a width of 1 meter around the flower bed. What is the area of the green belt?
中心小学有一个直径为8米的圆形花坛，现在准备在花坛外围修一条1米宽的环形绿化带．绿化带占地面积是多少？
<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<gadget id="calculator">3.14 * 25</gadget>
<output>78.5</output>

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

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

<gadget id="calculator">78.5 - 50.24</gadget>
<output>28.26</output>

<result>28.26</result>