Whats 5y³ - y² ? need this for assignment?

You cant answer that. If the problem is 5y^3 -y^2 = 0 then you could use the quadratic equation which would be y(5y^2 - y) = 0
the answer would be y(5y - 1 )(y) or y^2( 5y-1)

5y^3 - y^2
= y^2(5y - 1)

What is the question ?

What are the directions for the problem?
Factor? Find roots or zeros?
If its factor then y^2(5y-1)