The following table shows the distance travelled by one of the new eco-friendly energy-efficient cars travelled on gas.
| Litres of gas | 1 | 0.5 | 2 | 2.5 | 3 | 5 |
| Distance (km) | 15 | 7.5 | 30 | 37.5 | 45 | 75 |
Which type of properties are indicated by the table? How much distance will be covered by the car in 8 litres of gas?