By Vieta's, we have $r_1 + r_2 = - \frac{8}{1} = -8$ and $r_1 r_2 = \frac{4}{1} = 4.$
We also have $r_1 + r_2 = - \frac{16}{A}$ and $r_1 r_2 = \frac{B}{A}.$
Thus, we have $- \frac{16}{A} = - \frac{8}{1} \Rightarrow \frac{2}{A} = 1 \Rightarrow A = 2.$
We also have $4 = \frac{B}{A} \Rightarrow 4 = \frac{B}{2} \Rightarrow B = 8.$
$2+8 = \boxed{10}.$
I could've noted the fact that $a_{n-1} = \frac{b_{n-1}}{2},$ but visualizations are somewhat unreliable.