3. (30 points) A linked list is constructed to store integers. Each node is described by the following structure: struct node { int data; struct node *next; }; Assume a linked list containing a sentinel node is constructed from the above nodes. Write a C function named "sum prototyped as int sum(struct node* sent) that accepts a pointer to the sentinel node; adds the value of the positive data field in all (non-sentinel) nodes; and returns that sum as the function value. Only add the positive values; ignore any data value