simple harmonic motion

a) a mass of 25kg is supported by a vertical spring of stiffness 25kN/m and is acted on by a periodic force which has an amplitude 50N and frequency 5Hz. determine the steady state amplitude of the force vibration and the maximum force acting on the support point for the spring.

b) a horizontal platform rests on four vertical springs, each of stiffness 15kN/m and mass 0.25kg. what will the frequency of oscillation of the table be if it has a mass of 2.okg