Answer
$$-3y^3 -y^2 + 12y$$
Work Step by Step
Like terms must (1) be raised to the same power and (2) consist of the same variable (i.e. x and y are not like terms). It is also important to note that numbers are all like terms with each other when not multiplied by anything. Thus, combining like terms, we obtain:
$$ (-3)y^3-y^2 +(5+7) y \\ -3y^3 -y^2 + 12y$$
