A swimmer travels from the south end to the north end of a 30.0 m pool in 15.0 s and makes the return trip to the starting position in 19.0 s. What is the average velocity for the second half of the swim?
a. 1.60 m/s to the south
c. 1.60 m/s to the north
b. 2.0 m/s to the north
d. 2.0 m/s to the south