If the quadratic equation x^2 + 6x + k = 0 has roots that are both positive, what is the minimum value of k?
Answer: A. 9
For the roots to be positive, the sum of the roots (-b/a = -6) must be positive, and the product (c/a = k) must also be positive. The minimum value of k occurs when the roots are equal, which is at k = 9.