The $5.00 \mathrm{Vbattery}$ in Fig. E26.26 is removed from the circuit and replaced by a $15.00 \mathrm{~V}$ battery, with its negative terminal next to point $b$. The rest of the circuit is as shown in the figure. Find (a) the current in each branch and (b) the potential difference $V_{a b}$ of point $a$ relative to point $b$.