Use Vieta's formula for x² + px + q = 0. For this form, the sum of the roots is -p and the product of the roots is q. The given roots are 6 and -3, so their sum is 6 + -3 = 3. Since sum = -p, we have -p = 3, which gives p = -3. The product 6×-3 = -18 also matches the constant term, so the roots are consistent. Therefore the correct answer is -3.