A balanced lever has two weights on it, the first with mass #1 kg # and the second with mass #9 kg#. If the first weight is # 3 m# from the fulcrum, how far is the second weight from the fulcrum?

The torque or moment of each of the weights about the fulcrum is equal because the lever is balanced.
Torque= Fd
F= mg #m_1gd_1 = m_2gd_2#
F - Force (mass x gravitational
acceleration) #d_1 = m_2d_2/m_1#
(1kg)(3m)/9 kg