Hard Triple Beam Balance QUestion

[slydg895]

Alright guys here it is: My teacher asked us to think about a bonus question. He wants us to use torque to find the mass of the sliding mass on the center beam balance (the one that moves through 0,100,200...ect.) How do i do this?!

 

[Danger]

Even if it's a bonus question, it still belongs in the 'homework' section.
And, unfortunately, I haven't a clue as to offering you help with this.

edit: Wow, that was fast! By the time I posted, it had been moved. Still can't help you, though. Sorry.