Ram, Shyam and Hari went out for a 100 KM journey. Raman Hari started the journey in Ram’s car at the rate of 25 km per hour while Shyam walked at 5 km per hour. After sometime Hari got off and started walking at the rate of 5 km per hour and Ram went back to pick up Shyam. All three reached the destination simultaneously. The number of hours required for the trip was?