the phrase "x time later" is relative to a time that is not now, something that already occurred or will occur: - "he died. 3 days later, I went to Korea (to attend his funeral, etc)."

Once again, the expression in three days means "three days after now ", while three days later means "three days after then ". The preposition with which you confuse in is within (=inside the limits or extent of in time): within three days would mean "on any of the three days". F

is the correct answer. "in three days" means 3 days from today. "three days later" means 3 days after some time period that you were just talking about. You could use this if you had said, "I'm going away for 2 days. Elsa's birthday party will be held three days later".

three days away three days from now three days hence two days after 48 hours later