Two piers C and D are placed on a river, 1610 meter apart. Two people must make round trips from pier C to pier D and return. One person is to row a boat at a velocity of 6.4 km/hr relative to water, and the other person is to walk on the shore at a velocity of 6.4 km/hr. The velocity of the river is 3.2 km/hr in the direction from C to D. Find how long does it take each person to make the round trip?