perform the indicated operation
In order to combine the fractions you must make sure they have a common denominator.
So multiply the first term by (x-9)/(x-9) and the second by (x+9)/(x+9). After that combine like terms to get
x2 - 17x + 72 - (x2 + 14x + 36) all over (x-9)(x+9)
Now combine terms once again, foil the denominator and you get
-3x + 108/x2 - 81