When an undamped vibration absorber, having a mass \(30 \mathrm{~kg}\) and a stiffness \(k\), is added to a spring-mass system, of mass \(40 \mathrm{~kg}\) and stiffness \(0.1 \mathrm{MN} / \mathrm{m}\), the main mass ( \(40 \mathrm{~kg}\) mass) is found to have zero amplitude during its steady-state operation under a harmonic force of amplitude \(300 \mathrm{~N}\). Determine the steady-state amplitude of the absorber mass.