A \(1000 \mathrm{~kg}\) turbomachine has a rotating unbalance of \(0.1 \mathrm{~kg} \cdot \mathrm{m}\). The machine operates at speeds between 500 and \(750 \mathrm{rpm}\). What is the maximum isolator stiffness of an undamped isolator that can be used to reduce the transmitted force to \(300 \mathrm{~N}\) at all operating speeds?