Headwind, tailwind, groundspeed......
Example:
Distance 120NM, zero wind, speed 120 ( speedfactor 2, Groundspeed same).
Outbound 120/2 = 60 min.......inbound same = 120 minutes total flight time.
Distance 120NM, 30 headwind (dead on), speed 120, groundspeed 90 ( factor 1.5) = 120/1.5 = 80 minutes outbound.
Inbound same numbers except for tailwind ( groundspeed 150 = factor 2.5 ). 120/2.5 = 48 minutes = total flight time 128 minutes
Where did the 8 minuttes come from ? ;-)