what is logic?

Какое следующее число 4 6 15 105 ?

Where is LUC? please

How much time should it take for one to complete this game on easy?

I think the gamer deserves caring. There are a few features that are not deal breaker but certainly the absence of a map is not one of them. The inability to trace back clearly without a general map is horrendous, makes the sessions unnecessarily slow and long, a speed run is not possible and overall the experience becomes very tedious just guessing where to go next and have luck you get to the portal. I hope they enable one at some point before I lose my interest in the game......