jmc

We subtract $$\begin{array}{cccccc}& 3\cdot 7^2& +& 2\cdot 7& +& 1\\ -& (3\cdot 5^2& +& 2\cdot 5& +& 1)\\ & 3\cdot (7^2-5^2)& +& 2\cdot 2& & \end{array}$$Evaluating $3\cdot (7^2-5^2)+2\cdot 2$, we get $\boxed{76}$.