The equation of oscillation of a mass-spring system is x(t) = 0.3cos(4t - 0.7) where x is in meters and t in seconds. The spring constant is 15N/m. Find (a) the amount of mass M, (b) the total energy, (c) the earliest time ( t >0) when K.E. = 0.5 P.E., and (d) the acceleration of the mass at t = 0.08s. Assume 3 sig. fig on all quantities.