Only prog3/Makefile and prog4/prog4.c are modified.
In prog3/Makefile, it didn't build seperate programs for 32/64 bits, so it is modified similarly to prog2/Makefile.
In prog4/prog4.c, we are asked to use getrusage to retreive some runtime information. We calculated the system and user CPU time by a subtraction.
To clean all executables, run ./clean.sh at the root directory of the project.