#### Answer

$$9x^4+6x^2y+y^2$$

#### Work Step by Step

In order to solve this problem, we must use the FOIL method. This means that we multiply the first terms in each factor by each other. Then, we multiply the two outer terms by each other. Next, we multiply the two inner terms. Finally, we multiply the two terms that have yet to be multiplied by each other. Adding these together and combining like terms, we find:
$$ \left(3x^2\right)^2+2\cdot \:3x^2y+y^2 \\ 9x^4+6x^2y+y^2$$