Answer Happy

I am very lost and don't know where to start. Please show every step of the work. Will upvote if correct!
2) Solve the Spring/Mass system: A mass weighing 16 pounds stretches a spring feet. The mass is initially released from rest from a point 2 feet below the equilibrium position, and the subsequent motion takes place in a medium that offers a damping force that is numerically equal to the instantaneous velocity. Find the equation of motion if the mass is driven by an external force equal to f(t) = 10 cos 3t.