A boat takes a total time of three hours to travel downstream from P and Q and upstream back from Q to P. What is the speed of the boat in still water?

I. The speed of the river current is 1 km per hour.

II. The distance between P and Q is 4 km.

a) I alone sufficient while II alone not sufficient to answer

b) II alone sufficient while I alone not sufficient to answer

c) Either I or II alone sufficient to answer

d) Both I and II are not sufficient to answer

e) Both I and II are necessary to answer