To simplify the expression, we first expand the terms:

5(1-y)^2 = 5(1-2y+y^2) = 5(1-2y+y^2) = 5-10y+5y^2

(3+y)^2 = (3+y)(3+y) = 9+6y+y^2

3(1-y)(1+y) = 3(1-y^2) = 3(1-y^2) = 3-3y^2

Now, putting all the terms together:

5-10y+5y^2 - (9+6y+y^2) - (3-3y^2)

= 5-10y+5y^2 - 9-6y-y^2 - 3+3y^2
= (5-9-3) + (-10y-6y) + (5y^2-y^2+3y^2)
= -7 - 16y + 7y^2

Therefore, 5(1-y)^2-(3+y)^2-3(1-y)(1+y) simplifies to 7y^2 - 16y - 7.