I think that the problem wants the student to enter the schematic into Pspice and then use Pspice to do the DC analysis, finding all the currents and voltages.
Then do some simplification with source conversions.
For part 3 I think they want the student to use several different load resistors and use Pspice to determine the voltage across the various load resistors. Then working backward, knowing the voltage across a particular load resistor, the student can determine what the Thevenin equivalent of the given circuit must be. That Thevenin equivalent should be the same no matter what the load, and the problem wants the student to take that as proof that the Thevenin equivalent is the same no matter what the load resistor.
I'm not sure that is a rigorous proof, but I didn't write the problem.