"The point (1,8) is on the graph y=f(x). Find the corresponding coordinates of this point on each of the following graphs:

... c) y= -2f(-x)-7."

The textbook answer is (-1,9). I don't understand how they got this answer. The only way that that would make sense is if the corresponding y coordinate was doubled and positive, then subtracted by 7. But why would it be positive? The equation for corresponding coordinates is (x/k+d,ya+c) (where the parent function is y= af(k(x-d))+c). Accordingly, the y coordinate should be negative. Specifically, I think it should be -23.