Chapter 1 - Section 1.7 - Problem Solving: Interest, Mixture, Uniform Motion, Constant Rate Job Applications - 1.7 Asses Your Understanding - Page 142: 33

The width is $36$, the length is $78$

Let $x$ be the width, then $2x+6$ is the length and our equation becomes: $x(2x+6)=2808\\2x^2+6x-2808=0\\2x^2+78x-72x-2808=x(2x+78)-36(2x+78)=(2x+78)(x-36)=0$ Thus $x=-39$ or $x=36$, the earlier doesn't make sense, so $x=36$, thus the width is $36$, the length is $78$.