v in cubic feet (1 foot \ = 30.48 cm) is given for each of
a sample of 31 black cherry trees, and the height h in feet and
the diameter d in inches (1 inch = 2.54 cm) at a height 4.5 feet
above the ground.
data(trees)| [,] | d |
| numeric, diameter in inches | [,] |
| h | integer, height in feet |