Orchard Planting Problem/Classic Form/9

Classic Problem

$9$ trees are to be planted in an orchard so as to make the number of rows of $3$ trees the largest number possible.

That is:

$9$ points are to be configured in the plane so that the number of straight lines that can be drawn through exactly $3$ of these points is maximised.

Solution

The number of rows is $10$.

$\blacksquare$