so hiked 4km ----- 1 hour = 60 min.
14 km ----- x
--------------------------
x = 14*60/4 = 14*15 = 210 min. = 3 h 30 min.
and so again hiked 15 km by 5km/h
so 5km ------------- 1 hour =60 min.
12 km ------------ x
----------------------------
x = 12*60/5 = 12*12 = 144 min = 2 h 24 min.
so total 3 h 30 min. +2 h 24 min. = 5 h 54 min.