Functions: Let f(x/3) = x^2 + x + 1, and find sum of all z

[eouirai]

I'm in Algebra 2 right now and I don't get this problem.

Let the function for which f(x/3)= x^2 + x + 1. Find the sum of all values of z for which f(3z)= 7.
(a) -1/3 (b)-1/a (c)0 (d)5/a (e)5/3

 

[eouirai]

Now that I look over this question again, I think I get it now.
f(x)=9x^2 +3x +1
So set equations 9x^2 + 3x +1= 7
~9x^2 + 3x - 6
~3(3x^2 + x -2)
~3(3x - 2)(x +1)
so answer is 2/3 and -1?