$(10$ points$)$ Figure shows a small section of an electrical circuit. Find the potential difference between points A and $B(V_B-V_A)?$

Answer: $4$ V

$2.(10$ points$)$ Find the time constant of the RC circuit given in the figure.

Answer: $24$ ms

$3.(10$ points$)$ Figure shows a small section of an electric circuit. Find the potential difference between points A and $B(V_B-V_A)$ at the instant when the charge on the capacitor is $12C.$

$C=6F$

Answer: $22$ V