9. A museum exhibit hall is the shape of a regular octagon. The distance between any two parallel walls is 30 feet. What is the perimeter of the exhibit hall, rounded to the nearest foot?

Amass weighing 16 pounds stretches a spring 8/3 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 1/2 the instantaneous velocity. find the equation of motion if the mass is driven by an external force equal to f(t)=cos(2t).