6 kN/m and the damping constant of the damper is 400 Ns/m. If the mass is 50 kg, then the damping factor (d ) and damped natural frequency (fn), respectively, are

• A. 0.471 and 1.19 hz
• B. 0.471 and 7.48 hz
• C. 0.666 and 1.35 hz
• D. 0.666 and 8.50 hz