The circuit in the figure below includes a $12\mathrm{.}0-V$ battery with a finite internal resistance, $r=0\mathrm{.}720.($a$)(12)$

Find the current flowing through the $4\mathrm{.}00-$ and the $13\mathrm{.}2-$ resistors. $($b$)(4)$ How much current flows

through the battery? $($c$)(4)$ What is the potential difference between the terminals A and B of the battery?