кто шарит в алгебрепомогитетему не понялзадание не могу решить

1.
(y-y)/y=y*(y-1)/y=(y-1)/y.
(a-2a)/(a-4)=a*(a-2)/((a-2)*(a+2))=a/(a+2).
2. 
3/a+(a-3)/(a+5)=(3*(a+5)+a*(a-3))/(a*(a+5))=(3a+15+a-3a)/(a*((a+5))=
=(a+15)/(a+5a).
2x/(x-4)-2x/(x+2)=(2x/((x+2)*(x-2))=(2x-2x*(x-2))/((x+2)*(x-2))=
(2x-2x+4x)/(x-4)=4x/(x-4)
3.
(y-6y+9)/(y-9):(10x-30)/(y+3y)
1) (y-6y+9)/(y-9)=(y-3)/((y-3)*(y+3))=(y-3)/(y+3).
2) (10x-30)/(y+3y)=10*(x-3)/(y*(y+3)).
3) ((y-3)/(y+3)):(10*(x-3)/(y/(y+3))=(y-3)*y*(y+3)/((y+3)*10*(x-3))=y/10=70/10=7.
4.
x/y=a,  y/z=1/a       x/z - ?
y=z*a
x/(z/a)=a
x*a/z=a  a
x/z=1.

4. x = ay
z = 1/ay
x/z = (ay)^2