the condensed structural formula may be misleading; check out the full structural formula.
I see my problem now. Since the longest chain starts at the ethyl group at the very bottom and proceeds up and left, giving us
decane as the parent, only those two methyl groups branching off of carbon 3 matters. See I was thinking that it was supposed to be 3,3,3,3-trimethyl ethyl ethyl(?)
but that makes no sense at all.
It's all because those carbons in that branch are part of the
parent chain. doh!
btw thanks for the skeletal structure xiankai