Given the following declarations, write a function called listAvg () to determine the mean of all real-numbers stored in the list.

#define ARRAYSIZE 30 typedef struct Part { struct Part *next; double array[ARRAYSIZE]; } Part; typedef struct { Part *first; } List; Your function should take a single pointer to List and return a double . There should be no input or output. If the list is empty, your function should return zero. Assume the list has already been populated (i.e. filled-in/initialised).