Question 420313
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Hi
<img src="http://upload.wikimedia.org/wikipedia/commons/thumb/d/da/PerimeterRectangle.svg/200px-PerimeterRectangle.svg.png">

using x and y to represent the lengths of the respective sides.
 2x + 2y = 50m
 2x + 2*20 = 50m
    2x = 10m
     x = 5m