If the quadratic equation x^2 - 6x + 8 = 0 has roots r1 and r2, what is the value of r1 + r2?
Answer: B. 6
According to Vieta's formulas, the sum of the roots r1 + r2 is equal to the coefficient of x (which is -(-6)) divided by the coefficient of x^2 (which is 1), thus r1 + r2 = 6.