The variables a, b, and c represent polynomials where a = x^2, b = 3x^2, and c = x - 3. What is ab - c^2 in simplest form?
a. -8x^2 + 6x - 9
b. 8x^2 - 6x + 9
c. -2x^2 + 6x - 9
d. 2x^2 - 6x + 9