(4-3y)/(y+4) : ( (4-y)/(y+4) + y/(y-4) ) = (4-3y)/(y+4) : ( (4y-16-y²+4y)/(y-4)(y+4) + (y²+4y)/(y-4)(y+4) ) = (4-3y)/(y+4) : (4y-16-y²+4y+y²+4y)/(y-4)(y+4) =
(4-3y)/(y+4) : (12y-16)/(y-4)(y+4) = (4-3y)/(y+4) : 4(3y-4)/(y-4)(y+4) =
(4-3y)/(y+4) * (y-4)(y+4)/4(3y-4) = - (3y-4)/(y+4) * (y-4)(y+4)/4(3y-4) =
- (y-4)/4.