The side length of a square is 0.4 meters, which is equal to the perimeter of the rectangle, and the length of the rectangle is 0.5 meters, what is the area of the rectangle?
一个正方形的边长是0.4米，它与长方形的周长相等，长方形的长是0.5米，长方形的面积是多少．
<gadget id="calculator">0.4 / 2</gadget>
<output>0.2</output>

<gadget id="calculator">4 * 0.2</gadget>
<output>0.8</output>

<gadget id="calculator">0.8 - 0.5</gadget>
<output>0.3</output>

<gadget id="calculator">0.5 * 0.3</gadget>
<output>0.15</output>

<result>0.15</result>