A man is standing between two hills. He fires a gun. He hears two echoes: one after 0.3s and another after 0.5s. What is the distance between the two hills?

Amass weighing 24 pounds, attached to the end of a spring, stretches it 4 inches. initially, the mass is released from rest from a point 8 inches below the equilibrium position. find the equation of motion. (use g = 32 ft/s2 for the acceleration due to gravity.)