Hi, this is the general "Duolingo" forum, and most people on Duolingo do not study Spanish. Could you please edit your original post and use the drop-down list at top left to change the topic from "Duolingo" to "Spanish"? That way it won't clutter up the general forum, and the answers you get might help others who are learning Spanish and browse through the forum looking for new info.
OmegaGmaster has already answered your question - I'd just like to add that in Spanish, we use "el" before any feminine noun that begins with a stressed a sound:
el agua, las aguas
el hacha, las hachas
Área takes "el" in the singular, but it is a feminine noun. It's the remnant of "l'" that you find in other Romance languages, like l'aigua (the water in Catalan), l'eau (the water in French), etc.
When a feminine noun beginning with "a" or "ha" is pronounced with the stress on the first syllable, it uses "el" as the definite article instead of "la." (And "un" instead of "una")
El área (las áreas), el agua (las aguas), el alma (las almas).
Feminine words that start with an "a" ("ha") but don't have the emphasis on the first syllable use "la": la amiga, la alumna, la hamaca.