A rotating machine runs intermittently. When it is operating, it is rotating at 4200 rpm. The mass of the machine is 100 kg, and it is supported by an elastic structure with an equivalent spring constant of 160kN/m and a viscous damper of damping coefficient of 2400 N s/m that is in parallel with the spring. The engineer would like to keep the maximum transmission ratio less than 2.3 during the period that it takes the machine to reach the operating speed. If a spring is inserted in series with the damper, then what is the best value of the stiffness of this spring in order to have a TR <0.08 when the machine is at its operating speed?