A \(620-\mathrm{kg}\) fan has a rotating unbalance of \(0.25 \mathrm{~kg} \cdot \mathrm{m}\). What is the maximum stiffness of the fan's mounting such that the steady-state amplitude is \(0.5 \mathrm{~mm}\) or less at all operating speeds greater than \(100 \mathrm{~Hz}\) ? Assume a damping ratio of 0.08 .