Answer:
Explanation
I get the same answer you do, but I'm not at all certain I'm correct. I would have done it just as you did letting each y value define the new x value and then putting the - on the left in at the very end.
f(1) = 3
f(3) = -1
f(-1) = 7
But there is a minus in front of the left most f. That would make it - 7