1. **State the problem:** Find $i_0$ in the circuit using superposition, where $i_0 = i_c + i_x$. 2. **Turn off the 20 V voltage source to find $i_c$:** This means we replace the 20 V source with a short circuit. The circuit is shown in Fig. 4.10(a). 3. **Determine current $i_c$ from the 4 A current source:** Since the 4 A source is independent and directly sets current, we have $$i_c = 4 \text{ A}$$ 4. **Apply mesh analysis for loop with $i_c$:** For loop 2, according to equation (4.4.3): $$-3 i_1 + 6 i_2 - 1 i_1 - 5 i_2 = 0$$ Simplify: $$(-3 - 1) i_1 + (6 - 5) i_2 = 0$$ $$-4 i_1 + 1 i_2 = 0 \Rightarrow i_2 = 4 i_1$$ 5. **Turn off the 4 A current source to find $i_x$:** Replace the 4 A source with an open circuit and consider the 20 V voltage source active. 6. **Use mesh or nodal analysis to find $i_x$:** This step requires setting the dependent source equations and solving which is problem-specific. Usually, let mesh currents be $i_1$ and $i_2$ and write KVL/KCL to solve for $i_x$. 7. **Combine results:** Once $i_c$ and $i_x$ are found, compute $$i_0 = i_c + i_x$$ __Final answer depends on solving the second step equations specifically, but this outlines the method to find $i_0$ using superposition.__