I have a base rectangle with the size bx * by  and several rectangles which have all the same size ax*ay but can be arranged horizontally or vertically (ay*ax).

Is there a way to calculate the best arrangement?

how do I solve

x/(x-3) = y/(y-5)

manually?

How do I solve this system?

2x + z(2x-6) = 0

2y + 2yz       = 0

x-6x + y = -23

these mixed variables and terms confuse me.