9. (10 points) A 20 kg mass is attached to a spring with a stiffness 200 N/m and no external force. The damping constant b for the system is 140 N-sec/m. If the mass is displaced 25 cm to the right of equilibrium and given an initial velocity 1 m/sec to the left. (a) Find the equation of the motion. (b) Write the equation in the form y = A sin(wt + 6).