It is important to know that a Product is the result of a multiplication.
You have the following expression given in the exercise:
[tex]\mleft(3y+1\mright)\mleft(3y-1\mright)[/tex]Notice that it is the multiplication of two Binomials and it has this form:
[tex](a+b)(a-b)[/tex]By definition:
[tex](a+b)(a-b)=a^2-b^2[/tex]This is called "Difference of two squares".
You can identify that, in this case:
[tex]\begin{gathered} a=3y \\ b=1 \end{gathered}[/tex]Therefore, you get:
[tex]\mleft(3y+1\mright)\mleft(3y-1\mright)=(3y)^2-(1)^2=9y^2-1[/tex]The answer is:
[tex]9y^2-1[/tex]