WolframAlpha understands this input
solve {2 (L x^3/12+L x (W/2-x/2)^2)+(W-2 x)^3 y/6=B, 2 (W-2 x) y^3/12+(W-2 x) y (L/2-y/2)^2+x L^3/6=A},{x,y}
and runs this way
your problem here
I eliminated all the () that I thought were not absolutely necessary to make the input a little shorter, because there is a line length limit on WA input. That may not have been absolutely necessary, but I have a personal set of rules that I use when trying to make WolframAlpha understand and work for me..
Unfortunately, the free version I am using here runs out of free time before it completes, but it does provide a lot of information about the solution before it quits.
The output includes multiple "Root" expressions. Those are a shorthand notation that Wolfram sometimes uses for roots of polynomials that are complicated enough that it sometimes can't display as simply as the two solutions to a quadratic equation. It is doing that because, instead of your problem being a quadratic equation, it appears to be in the form of 9th degree polynomials and it is trying to give you an exact expression for each of those roots, "Root" is documented here RootDocumentation
You may be able to interpret some or all of what you need from that output. If that isn't enough then you might be able to scrape all that output and try a fresh session of WA where you paste an individual Root expression and see whether that will allow you to build up individual parts of your solution and then assemble them into a complete solution.
I hope this helps.