Solve the indicated or given systems of equations by an appropriate algebraic method.
Find the voltages $V_{1}$ and $V_{2}$ of the batteries shown in Fig. $5.28 .$ The terminals are aligned in the same direction in Fig. $5.28(\mathrm{a})$ and in the opposite directions in Fig. $5.28(\mathrm{b})$. (FIGURE CANNOT COPY)