which of the following best describes the effect of replacing the graph of y = f(x) with the graph of y= f(x) - 9? a. the graph of y = f(x) will shift up 9 units b. the graph of y = f(x) will shift down 9 units c. the graph of y = f(x) will shift left 9 units d. the graph of y = f(x) will shift right 9 units