To factor out x2 + bx + 16, the easiest way is to find out 2 different values that will add up to b but when multiplied is positive 16. Given that the only solution to this equation above is x = 4. the factored out form should be (x - 4)^2 or (x-4)(x-4). As b should be the addition of these two x values, b should be -8. The correct option is the second option, b = -8.