"We are waiting for that boy and for that automobile."
Translation:Čekáme na tamtoho hocha a na tamten automobil.
Because it is a translation of that in the correct form for masculine inanimate singular accusative while tamtoho hocha is animate. Nothing more can be said unless you tell us why what else would you expect instead.
Looks like your answer got deleted, because I have rewritten and deleted my post. Sorry, I did that at the same time you answered and I got the email notification about your answer only after pressing delete.
It is not neuter. The similarity of the word root is irrelevant, so there is really no connection with the fact that auto is neuter and automobil masculine. A related older word lokomobila (a portable engine, https://en.wikipedia.org/wiki/Locomobile ) is feminine because of the ending. Anything can happen.
Words ending with -il tend to be masculine. Foreign ones: mobil, decil, debil... Native ones derived from verbs (past participles): slídil, chlubil...
Duo suggests as a right answer "čekáme na toho kluka a na tamo auto", it has to be tamto, not tamo. Another wrong sentence proposed to me: "čekáme na tamoho kluka a na tamo auto."
Yep. We already have some '"Correct Solution" is unnatural or has an error' reports, but they are almost useless, because we have no idea which solution is it referring to. Thanks, we will fix it.