Three survey boats complete routes across a reservoir. Their journey data are shown in the table.
| Boat | Journey data |
|---|---|
| A | Travels a total distance of 0.90 km; it is moving for 3.0 minutes and stationary for 20 s |
| B | Travels 1.68 km in 6.0 minutes |
| C | Has an average speed of 17 km/h |
During a second test lasting 7.5 minutes, each boat has the same average speed as for its first route.
Calculate how much farther the fastest boat travels than the slowest boat during the second test.