Answer :
ANSWER
Option B
[tex]\begin{equation*} \left(7x+9y\right)\left(7x-9y\right) \end{equation*}[/tex]EXPLANATION
Given;
[tex]49x^2-81y^2[/tex]Factor out ;
[tex]\begin{gathered} 49x^2=(7x)^2 \\ 81y^2=(9y)^2 \\ \left(7x\right)^2-\left(9y\right)^2 \end{gathered}[/tex]Now, we have;
[tex]\left(7x\right)^2-\left(9y\right)^2[/tex]Using difference of two squares;
[tex]\begin{gathered} x^2-y^2=(x+y)(x-y) \\ (7x)^2-(9y)^2=\left(7x+9y\right)\left(7x-9y\right) \end{gathered}[/tex]