A person can swim in still water at 10 km/h. If the speed of water 4 km/h, how many hours will the man take to swim back against the current for 12 km?  Choose the correct option
A) 2  B) 7  C) 5  D) 9  E) 6

Rationale: "m = 10 s = 4 us = 10 - 4 = 6 d = 12 t = 12 / 6 = 2 answer : a"
Answer: A