6. Here is a modified version of Exercise 5. Let f : Z -> Z, f(x) = x2. (Carefully note the domain and codomain!) (a) Let S = {-5, -4, 0, 1, 5, 9). Compute f[S]. (b) Let 7' = (-9, -7, 0, 1, 7, 16). Compute f-'[7']. (c) What is the range of f? (Is it easy to describe?) (d) Sketch a reasonable portion of the graph of f