For question #95 from the Physics question pack, I am good with the beginning steps of the problem and with the concept that the torque in the clockwise direction must equal the torque in the counterclockwise direction. However, I am confused as to when they are calculating the torque for the weight of the meter stick and use the value of 20cm. This value is the length between the suspension and the centre of mass of the metre stick but I am not sure how to find the centre of mass.