Sorry about the late answer, our IT conection dropped - for 11 days!!
This is a little tricky for me, because in my culture we never ask 'how are you' as a greeting, and I have to guess a little here.
It is my impression that "how are you" is a greeting similar to 'goddag' (good day) a culturally consensus of how to greet someone politely. Not meant as an actual question about your life or well being.
So I'd say you simply say 'fine, and you?' not expecting the other to actually tell you how they are either.