In Exercises 7-10, find the zeros of the function. Then sketch a graph of the function.

7. f(x) = - 5x ^ 4 + 20x ^ 3 + 60x ^ 2

8. g(x) = - x ^ 3 - x ^ 2 + 30x

9. k(x) = x ^ 3 + x ^ 2 - 4x - 4

10. f(x) = x ^ 1 - 4x ^ 2 - 9x + 36