"Seth has a scarf."
Translation:عِنْد سيث وِشاح.
Hmm, the uninflected عند would be the only correct form in this sentence...unless you changed the word order. Did you have "سيث عِنْد وِشاح"? In that case, you might need "عِنْدَهُ", but I'm not certain that's correct. If you stick with the order in the solution at the top of the page, you don't need to change عند. Hope that helps.
And helpful tip, only verbs (in any language) are conjugated. Other parts of speech declined, or more broadly, inflected. "عند" in Arabic functions as a preposition.