A boat moves 3km east in 10min, then 4km north in 20min, and finally 3km west in 10min. Which option shows the correct average speed and the magnitude of the average velocity for the complete journey?
(a) 16km/h,6km/h
(b) 6km/h,15km/h
(c) 15km/h,6km/h
(d) 15km/h,4km/h