Please solve

Note: The information of this problem might be repeated in several questions. The bicycle renting company at the university has several parking stations that are located on the main entrance, the mall building, the engineering building and the medicine building. The renting company allows one and two-way rentals so that bikes rented in one station may end up in different one. Historical data show that at the end of each day 15% of the rental are two-way. As for the one-way rental, from the main entrance station 30% go to medicine building, 20% go to engineering and the rest goes to the mall. From the mall, 25% go to medicine and the rest goes to engineering. From engineering, 40% go to the mall, 15% to medicine and the rest goes to the main entrance. Finally, from medicine, 20% go to engineering, 40% to the mall and the rest goes to the main entrance. On average, how long it takes for each bike at the medical building to return to its original location (in days)