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.
What is the volume of the tank?