Question 391536
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Hi,         
<img src="http://upload.wikimedia.org/wikipedia/commons/thumb/d/da/PerimeterRectangle.svg/200px-PerimeterRectangle.svg.png">
Hi,         
Let x AND 2x represent the width and length respecively
Question states;
 2(2x) + 2x = 420
 4x + 2x = 420
     6x = 420
      x = 70, the width.  Length is 140   (2*70)
Applying the Pythagorean theorem
 70^2 + 140^2 = d^2
        156.5248 is the length of the diagonal