1. The problem statement, all variables and given/known data 2. Relevant equations 3. The attempt at a solution I set up my problem as : (12kg x .5m) + ( 1/3 x 4kg) = (1.05m x Mass) + (2/3 x 4kg) then , i just solve for mass, is that correct? actually, should I change the (1/3 x 4kg) to ( 1m x 4kg) and the (2/3 x 4kg) to ( 2m x 4kg)?