If 4^4y = 16^3y-2, what is the value of y?

I think you meant:

4^(4y) = 16^(3y-2)
4^4y) = (4^2)^(3y-2)
4^(4y) = 4^(6y-4)
6y-4 = 4y
2y=4
y = 2