The logarithmic decrement of a spring mass-dashpot system

Question

A vibratory system consists of a mass 12.5 kg, a spring of stiffness 1000 N/m, and a dashpot with damping coefficient of 15 Ns/m

(2)    The value of logarithmic decrement is                                                                                                                                     

(a) 1.35                           (b) 0.42                        (c) 0.68                           (d) 0.66