The perimeter of a rectangle is 50 decimeters, and the ratio of length to width is 4:1, what is the area of the rectangle?
一个长方形的周长是50分米，长和宽的比是4：1，这个长方形的面积是多少．
<gadget id="calculator">50 / 2</gadget>
<output>25</output>

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

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

<gadget id="calculator">5 * 4</gadget>
<output>20</output>

<gadget id="calculator">20 * 5</gadget>
<output>100</output>

<result>100</result>