jmc

Expanding the product on the left gives $0.03n+0.08\cdot 20+0.08n=12.6$. Simplifying the left side gives $0.11n+1.6=12.6$. Subtracting 1.6 from both sides gives $0.11n=11$, and dividing by 0.11 gives $n=\boxed{100}$.