Final answer:
To find the current i using the principle of superposition, add the individual currents due to each source algebraically. This requires turning off all but one source at a time and using Kirchhoff's rules to solve for the currents.
Step-by-step explanation:
To use the principle of superposition to find the current i in a circuit, you would add the individual currents due to each source algebraically. Hence, the correct answer is:
A. Add the individual currents due to each source algebraically.
Superposition involves analyzing the contribution of each independent source (voltage or current) in the circuit separately. You would turn off all other independent sources (by replacing voltage sources with a short circuit and current sources with an open circuit) and calculate the current due to the one active source. After doing this for each source separately, you then algebraically sum the currents to find the total current i in the branch of interest. This approach requires the use of Kirchhoff's rules - the junction (or node) rule and the loop rule, to set up simultaneous equations that can be solved to find the currents.