A 65 kg person wants to try bungee jumping. He went to an adventure park with a bungee jumping activity. Then, he jumped from a very high bridge where the bungee rope is tied, reaching the lowest point 8 times through the process of oscillation that spends 38 seconds. The terrifying activity comes to a stop while the person is hanging 25 meters below the level of the bridge. Calculate the spring stiffness constant and the unstretched length of the bungee rope. Assume that the oscillation follows simple harmonic motion.