Triangle xyz is dilated with the center of dilation at the origin to produce triangle x'y'z'. triangle xyz is similar to triangle x'y'z'. the scale factor used to dilate triangle xyz to produce triangle x'y'z' is?

Atourist boat is used for sightseeing in a nearby river. the boat travels 2.4 miles downstream and in the same amount of time, it travels 1.8 miles upstream. if the boat travels at an average speed of 21 miles per hour in the still water, find the current of the river.