Hey Neil123.
S_9 - S_5 should include the 6th, 7th, 8th, and 9th terms (assuming the first term is S_1, otherwise it will be 10th, 9th, 8th, and 7th terms).
Calculate the sum between the terms t_{5} and t9 of the geometric sequence in which the 4th term is -9/8 and the 7th term is 8/3. I find it confusing since I don't know which terms to find the terms for. Is it S_{9}-S_{5} or is the sum only for the terms 6,7 and 8?