urgent c programming please solve in one hour

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).

(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.