If an American elm and a shagbark hickory each currently have a diameter of 1.5 feet, what will be the closest difference, in inches, of their diameters 12 years from now? (1 foot = 12 inches)
| 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 |
1.3
1.4
1.5
1.6
