Decay Time of Damped Oscillator

Classical Mechanics

A $10 \text{ kg}$ mass is attached to a spring of spring constant $10 \text{ N}/\text{m}$ . The entire system is submerged in water, which exerts a viscous damping force on the mass $F_d = -(2 \text{ N}\cdot \text{s}/\text{m}) \:v$ . The mass is pulled so that the spring is displaced from equilibrium by $.1 \text{ m}$ and is released. Find the $1/e$ decay time of oscillation in seconds.