y-(4x-((y-x)-7x)) = y-(4x-(y-x-7x)) = y-(4x-(y-8x)) = y-(4x-y+8x) =

= y-(12x-y) = y-12x+y = 2y-12x

y-(4x-((y-x)-7x)) = y-(4x-(y-x-7x)) = y-(4x-(y-8x)) = y-(4x-y+8x) = 2y-12x