jmc

First, we combine like terms in the expression: $$\begin{array}{rl}& (6a^3+92a^2-7)-(-7a^3+a^2-7)\\ & =6a^3+92a^2-7+7a^3-a^2+7\\ & =13a^3+91a^2.\end{array}$$We can factor out a $13a^2$ from the expression, to get $$13a^3+91a^2=\boxed{13a^2(a+7)}.$$