Based on the table, what is the expected increase in the diameter (in inches) of a river birch tree with a current age of 42 years over the next 7 years? Use the growth factor for river birch.
| Species of tree | Growth factor |
|---|---|
| Red maple | 4.5 |
| River birch | 3.5 |
| Cottonwood | 2.0 |
| Black walnut | 4.5 |
| White birch | 5.0 |
| American elm | 4.0 |
| Pin oak | 3.0 |
| Shagbark hickory | 7.5 |
1.0
1.5
2.0
2.5
