Let $f ( x ) = \frac { x ^ { 3 } - 3 x ^ { 2 } } { 36 x - 108 }$

Let $f ( x ) = \frac { x ^ { 3 } - 3 x ^ { 2 } } { 36 x - 108 }$ . For what values of x is $f ( x ) = 1$ ?