you ned to see the no. of group attached
well there is correction in ex.
it should have been
| 7 6 5 4 3 2 1 C--------C---------C-----------C-------C--------C-------C | | | CH3 CH3 CH3 | |
1,2,6 or 2,6,7
so now 1+2+6=9 and 2+6+7=15
you will have to take the one with lower sum i.e. 1,2,6
this is lowest sum of locant rule