Answer
$$4y^2 + 2y$$
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:
$$ y^2 + 2y+3y^2 \\ 4y^2 + 2y$$
