Two residences, Ion Residences (located upstream) and Omega residences (located downstream) are located along a riverside. The distance between the two residences is 1800 m. Diego and Paul must make round trips between the two residences, starting from the Ion Residences. Paul is paddling a canoe at a constant speed of 4.50 km/h relative to the water in the river. On the other hand, Diego walks on the riverside at a constant speed of 3.7 km/h. The velocity of the river is 2.60 km/hr in the direction from Ion to Omega. How long will it take for Paul and Diego to make the round trip?