If you need to find a weight and moment after the seats are removed you will need to know which seats are to be removed. That would have to be given in the question. Let's imagine that we are removing all of the seats except the pilot's seat and leaving them behind in the hangar.
From the supplement on the bottom of page 17 we are told that each seat weighs 5kg. The table in paragraph 5.4 on page 17 gives the arm of each row.
Find the moment generated by each seat by multiplying each arm by the weight of the seats missing in that row.
Row 1 5 x 2290 = 1.145 [after dividing by 10,000]
Row 2 10 x 3300 = 3.3
Row 3 10 x 4300 = 4.3
TOTALS 25kg and 8.745. To get the new weight subtract 25kg from the basic empty weight given and subtract 8.745 from the basic empty moment given.
This gives the 'Operating weight' for that flight. If you are going to take the seats with you in the rear compartment, add the 25kg back in along with the moment generated by 25kg in the rear compartment. 25 x 5000 = 12.5.