A circular cardboard with a diameter of 80 cm has the same area as a rectangular cardboard with a length of 20 cm. What is the width of the rectangle in centimeters?
一个直径为80cm的圆形纸板与一个长为20cm的长方形纸板面积相等．求长方形宽是多少厘米？
<gadget id="calculator">80 / 2</gadget>
<output>40</output>

<gadget id="calculator">40 ** 2</gadget>
<output>1_600</output>

<gadget id="calculator">1_600 / 20</gadget>
<output>80</output>

<gadget id="calculator">3.14 * 80</gadget>
<output>251.2</output>

<result>251.2</result>