An \(81\,\text{kg}\) student dives off a \(45\,\text{m}\) tall bridge with an \(18\,\text{m}\) long bungee cord tied to his feet and to the bridge. You can consider the bungee cord to be a flexible spring. What spring constant must the bungee cord have for the student's lowest point to be \(2.0\,\text{m}\) above the water?