The question is asking us to find the value of b in the function: f ( x ) = x^2 + b x + 10, if the axis of symmetry is x = 6. This is a quadratic function in a form: f ( x ) = a x^2 + b x + c. The formula for the axis of symmetry is: x = - b / 2 a. So: 6 = - b / 2 a; 6 = - b / 2 ; - b = 6 * 2; - b = 12. Answer: b = - 12.
