A wire encloses a circle with a radius of 4 decimeters. If this wire forms a square, what is the area of the square?
一根铁丝正好围成一个半径4分米的圆，如果把这根铁丝围成一个正方形，这个正方形的面积是多少平方分米．
<gadget id="calculator">2 * 3.14 * 4</gadget>
<output>25.12</output>

<gadget id="calculator">25.12 / 4</gadget>
<output>6.28</output>

<gadget id="calculator">6.28 * 6.28</gadget>
<output>39.4384</output>

<result>39.4384</result>