The equation will simplify to a linear equation in n, which can be solved to find n.
n² +6n +8 = (n -2)(n -9) . . . . . . we assume this is your intent
n² +6n +8 = n² -11n +18 . . . . . . expand the right side
17n = 10 . . . . . . . . . . . . . . . . . . . add 11n -8 -n² to both sides
n = 10/17 . . . . . . . . . . divide by the coefficient of n
The number that makes the equation true is n = 10/17.
