"The years of the 80's" should be accepted. It's confusing when you know what it means but you don't know whether duolingo will accept your answer. I spent a good three minutes trying to decide what to put here. I though the eighties would not be enough becuse you used "annees" in the sentence. If you want 'the eighties' just say les quatre-vingts.
it is always annoying, when you spend more time thinking about the Duolingo-logic than about an actual translation ;)
Anybody care explaining to my slow logic how quatre and vingt suddenly make eighty?