Without any more information we can't find the actual numerical representation of the length and width but we can give an expression that will allow us to find them...
We let the width equal x, so the length is 3x. That would be the dimensions...
length = 3x
width = x
So to find perimeter the expression would be
2(3x) + 2(x) =
6x + 2x =
8x
For the area it would be
a= length × width
a = 3x × x
a = 3x^2