Trying to solve the following problem based on the below program. It's from Chapter 2 in Computer Systems (Fourth Edition) by J. Stanley Warford.

Section 2.4 . The function s um in Figure 2.25 is called for the first time by the main program. From the second time on it is called by itself. *(a) How many times is it called altogether? (b) Draw a picture of the main program variables and the run-time stack just after the function is called for the third time. You should have three stack frames. (c) Draw a picture of the main program variables and the run-time stack just before the return from the call of part (b). You should have three stack frames, but with different con- tents from part (b)