Doing your duty. The problem arises to what end are you doing your duty. Really, I suppose that’s the problem with reasonable answers to the question. All we’re really doing is giving means to an end, not exactly dealing with the end result at all. If the meaning of life is to attain wealth and prestige, your only opening yourself up to another question; what does a person gain by manner of this wealth and prestige? How does what they gain give their life “meaning”?
The most predictable answer would be happiness. The problem with that is the happiness which could be gained from this is subjective, so how could we really say it qualifies as the correct answer to such a question?
But, eh, that’s just Philosophy class messing with me, it’s obviously an anything goes question that’s meant to deal with people’s views, so I’ll stick with duty. It seems like the least self-serving and possesses the most potential to have a good result, except, maybe helping others.