What are the possible rational zeros of f (x) = x4 + 2x3 - 3x2 - 4x + 18?

The number of roots of any polynomial is given as the order of the polynomial. For n-order polynomial, the minimum number of roots are "n'. Given, f (x) = x^4 + 2x^3 - 3x^2 - 4x + 18, it has minimu of four roots. The given expression has the following roots ± 1, ± 2, ± 3, ± 6, ± 9, ± 18