It's not wrong M=17
All the hanging weights can be calculated according to there mass as I-try states.There mass is centred around the hanging bar.
The positions of the weights can be simplified to half the distances ie:- The unknown mass on the left is at point 1 instead of 2 and the other masses on the right are at 1and 3 instead of 2and 6.
So a mass of 5 on the right at position 3 will lift 15 on the left at position 1
and a mass of 2 on the right at position 1 will lift 2 on the left at position 1
makeing a total of 17.
