A landing deck, which can be modelled as a single DOF system, is deflected at its midspan and released. After the initial disturbance, the amplitude of 20 mm was decayed exponentially to 12 mm and the frequency was measured as 1.65 Hz. When a vehicle having a mass of 40 tons was located at the midspan, the frequency was measured as 1.45 Hz. Determine (a) the mass (b) stiffness and (c) the damping ratio of the structure