The first equation is x+x+3x+3x. You know that the perimeter is w+w+l+l, so, you can simply substitute the width, x, and the length, 3x (Three times the width).
The second equation is 8x. This comes from the first expression. If you have three of something plus three of the same thing plus one of the same thing plus one of the same thing, you have 8 of that thing. In other words, combine like terms.
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