Problem 4. An object weighing 4 pounds is attached to a spring and stretches it 6 inches. The object is released from a position 4 inches below its equilibrium position with an upwards initial velocity of 2ft/s². Assume there is no dampening of the spring motion. (a) Calculate the spring constant of the spring and mass of the object attached to it, both in appropriate units. (Please use g = 32ft/s² for the approximate acceleration of an object due to earth's gravity). (b) Model this situation as a second-order initial value problem involving u(t), the position of the mass relative to its equilibrium position t seconds after being released. (c) Solve your IVP to determine the position u(t) of the mass at any time t. (d) Determine the frequency, period, amplitude of motion. Label your answers clearly.