Dig a reservoir with a depth of 5 meters and a diameter of 8 meters at the bottom. What is the area of the reservoir in square meters?
挖一个深5米，底面直径8米的蓄水池，水池的占地面积多少平方米．
<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>

<result>50.24</result>