Answer
$9a^{2}-4c^{2}$
Work Step by Step
From Page 301, we know that the product of a sum and difference of two terms $x$ and $y$ is given by the following equation: $(x+y)(x-y)=x^{2}-y^{2}$.
Therefore, $(3a+2c)(3a-2c)=(3a)^{2}-(2c)^{2}=3^{2}a^{2}-2^{2}c^{2}=9a^{2}-4c^{2}$.