urgent c prorgramming 1 hour pls fast extremely urgent

Consider the following recursion: int f(int n) { if (n == 0) return 0; if (n == 1) return 0; if (n == 2) return 1; return f(n-1) + f(n-2) - f(n-3); }

(a) Determine the values of f(3) and f(4). You must show your steps to obtain any credit for this question

(b) From your observation of part (a), determine f(101).

(c) Including the first one, how many calls on f() are made to compute f(7)?

(d) Write a non-recursive function to achieve the achieve the same operation.