Only need answer to 2.4 please :) its for a practise set

Assume there is a software project with three programmers: P1, P2, and P3. P1 is the team leader and is interested in constructing a project that facilitates development of a complex application written in C. P1 decides that this should be a modular program and that a makefile should be used (A) Write a makefile that satisfies these concerns: . P1 programs: main.c and database.c. P1 needs access to menu.o . P2 programs: menu.c and divide+conquer.c. P2 needs access to all of P3's programs and P1's database.o from divide+conquer.c P3 programs: fact.c, fib.c, csv.c, and library.c . Minimize the number of source files needed (both .c and .h) . Compile should be as quick as possible . There needs to be an optional feature to backup files into a directory called mybackup creating that directory if it does not already exist in the current directory . There needs to be an optional delete all the .o files feature (B) P1 wants to make sure that no one includes the same header file twice. Give an example of how to write a header file so that the file cannot be loaded twice during compile