[tex]\bf \boxed{-9}\rule[0.35em]{9em}{0.25pt}-2\rule[0.35em]{1em}{0.25pt}\stackrel{\stackrel{midpoint}{\downarrow }}{-1.5}\rule[0.35em]{1em}{0.25pt}-1\rule[0.35em]{2em}{0.25pt}0\rule[0.35em]{10em}{0.25pt}\boxed{6}[/tex]
from -9---------------------------0------------------6, there are 9+6 units, namely 15, half that is 7.5, 7.5 units from -9 is -1.5.
