To solve this problem, we need to find a common denominator for all the fractions.

First, we need to find the least common multiple (LCM) of 12, 24, 18, and 9. The LCM of these numbers is 72.

Now, we need to rewrite each fraction with the denominator of 72:

5/12 = (5 6) / (12 6) = 30/72
11/24 = (11 3) / (24 3) = 33/72
17/18 = (17 4) / (18 4) = 68/72
7/9 = (7 8) / (9 8) = 56/72

Now, the expression becomes:

30/72 + 33/72 - 68/72 - 56/72

Combining the fractions:

(30 + 33 - 68 - 56) / 72
(63 - 124) / 72
-61 / 72

Therefore, the simplified answer is -61/72.