Why not "what decade..."
That's "jaka". We try to keep them apart, they're problematic enough without mixing them.
The one with all the wars, good food, imminent end of the world, laughing children and stupid politicians. Oh wait! :D
In French a "décade" is 10 days where in English a "decade" is 10 years (in French it's a "décennie").
From the clothes and hairstyle I'd say... (fill in the blank)