2. Use superposition to calculate the current through the 1.0kΩ resistor in the circuit shown below (show all work):

Answer:
2.5mA
Explanation:
The principle of superposition states that
instead of having to solve for the voltage/current through a resistor when all the power source are there, you're allowed to solve for the voltage/current through a resistor for each independent source separately and add them up in the end later for the final result.
General Step of Solving:
So.
1.) Solve for voltage through the 1k resistor when only the 15V source is on. i.e. turn off the 10V source.
2.) Solve for voltage through the 1k resistor when only the 10V source is on. i.e. turn off the 15V source.
3.) Add up the two voltage you found together.
You should get V_1k = 2.5V
so the Current through it must be I_1k = 2.5/1k = .0025A = 2.5mA