You have the following expressions given in the problem above:
(y^2/y-3)(y^2-y-6/y^2+y)
By applying the exponents properties, you can simplify it, as it shown below:
(y^2/y-3)(y^2-y-6/y^2+y)
(y^4-y^3-6y^2)/(y^3+y^2-3y2-3y)
(y^4-y^3-6y^2)/(y^3-2y2-3y)
Then, you have:
y^2(y^2-y-6)/y(y^2-2y-3)
(y^2-y-6)/(y^2-2y-3)
The answer is: (y^2-y-6)/(y^2-2y-3)