daniloromero X/(y-4)=x/y+30
x/(y-4)=(x+30y)/y
xy=(x+30y)(y-4)
xy=xy+30y²-4x-120y
30y²-4x-120y=0
4x=30y²-120y
x=(30y²-120y)/4

(30y²-120y)/(y-4)=[(30y²-120y)+30]/y
(30y²-120y).y=(30y²-90y).(y-4)
30y³-120y²=30y³-90y²-120y²+360y
90y²=360y
y=360/90
y=4

x=(30.4²-120.4)/4
x=(480-480)/4
x=0

x/y=z
z=0/4
z=0