Compare the motion of three speedboats. Which speedboat was moving at the highest speed?

 - a speedboat that moved 235kilometers east in 5hours
 - a speedboat that moved 390kilometers east in 5hours
 - a speedboat that moved 330kilometers south in 5hours
Look at the distance each speedboat moved and the time it took to move that distance. The direction each speedboat moved does not affect its speed.
Notice that each speedboat moved for 5 hours. The speedboat that moved 390 kilometers moved the farthest distance in that time. So, that speedboat must have moved at the highest speed.