Write 3 versions of function DoublePlus(n) to be embedded in the program (at red box in Figure 1). All versions are written in Pure C (except for the single asm() statement to capture and save the sp). All versions receive n as an argument and return the value of the recurrence DoublePlus(n). (a) (8) Write an empty version of DoublePlus() that does nothing except capture the sp and return a constant. This will be useful for testing and debugging your main program, and also for calculating the fixed overhead delays in your elapsed time calculations. (b) (8) Write a version of DoublePlus() as a non-recursive iterative loop to return the value of DoublePlus(n). (c) (16) Write a version for which DoublePlus() is a recursive function (one that calls itself for each step) to eventually return the value of DoublePlus(n).