If one root of the quadratic equation x² - 7x + k = 0 is 3, what is the value of k?
Answer: B. 9
Using the fact that if one root is 3, then the other root can be found using the sum of roots: 3 + r = 7, hence r = 4. The product of the roots is 3 * 4 = 12, which gives k = 12.