The error was "+(-x^2)" was change to a "-x^2" and that it was only 1 negative real root.
The correct change was "+(-x ^2)" to "+x^2" and that there are 3 negative real roots instead of 1.
First you would break down the problem into a brace map so you would know what to look for and know what the problem already has. Then you would work out the problem using the area and set it equal to "y" then sove. Add the height to the width and length. So the dimensions would be height(h)=6, width(2h)=12, length(w+4)=16.