A group of astronomers compiled data on several distant galaxies to study the expansion of the universe. Figure 1 shows a scatter plot of their distance from Earth against their recessional velocity, with a line of best fit drawn.
Galaxy Data
| Distance from Earth (Mpc) | Recessional velocity (km/s) |
|---|---|
| 4.0 | 250 |
| 6.5 | 500 |
| 8.0 | 520 |
| 11.0 | 850 |
| 12.5 | 780 |
| 15.0 | 1150 |
| 17.5 | 1200 |
| 20.0 | 1500 |
| 22.0 | 1450 |
| 24.0 | 1850 |
Use Figure 1 to estimate the recessional velocity of a galaxy that is 18 Mpc away from the Earth.