Ok so, you need an equation and here it is:
Length×Width=Area
L=(W×2) Because you don't know what the actual number is. Plug that into the first equation.
(W×2)×W=288
2w×w=288
2w^{2}=288
divide both sides by 2
w^{2}=144
Square root both sides
\sqrt{w^{2}} = \sqrt{144}
w=12
Now we need to solve for length, that's easy
Plug the width in the first equation L×12=288
L=24
Have a good day!