Mechanical vibration

A refrigeration unit of 5 Tons is supported by six springs with 60 mm static deflection. The unit is running at 60 Hz. What will be equivalent stiffness of 6 springs?
2.
The seat of a van, with the passenger, weights 2500 N and is found to have a static deflection (δst.) of 15 mm under its own weight. The vibrations due to unbalance wheels alignment is transmitted to the base of the seat as harmonic motion with frequency 10 Hz and amplitude of the base displacement (Y) is found to be 2 mm. RMS value of amplitude of the displacement (mm) to be felt by the passenger is.
3.A steel shaft of diameter 1.5 cm and length l m is supported at the two ends in bearings. It carries a turbine disc, of mass 15 kg and eccentricity 0.003 m, at the middle and operates at 5000 rpm. The damping in the system is equivalent to viscous damping with ζ = 0.015