A machine of mass 520 kg produces a vertical disturbing force which oscillates sinusoidally at a frequency of 25 Hz. The force transmitted to the floor is to have an amplitude, at this frequency, not more than 0.4 times that of the disturbing force in the machine, and the static deflection of the machine on its mountings is to be as small as possible consistent with this. For this purpose, rubber mountings are to be used, which are available as units, each of which has a stiffness of 359 kN/m and a damping constant of 2410 Ns/m. How many of these units are needed