Read the passage below and solve the questions based on it.
The tank at a water supply station is filled with water by several pumps. At first, three pumps of the same capacity are turned on; 2.5 hours later, two more pumps (both the same) of a different capacity are set into operation. After 1 hour, the additional pumps were set into operation; the tank was almost filled to its capacity (15 m3 were still lacking); in another hour the tank was full. One of the two additional pumps could have filled the tank in 40 hours.
How much water does one of the first three pumps fill in an hour?