I need help with this question (Geometry)

Kelli swam upstream for some distance in a hour.she then swam downstream the same river for the same distance in only 6 minutes.if the river flows at 5km/hr, how fast can kelli swim in still water?

Enter your answer and show all the steps that you use to solve this problem in the space provided. write a list of steps that are needed to find the measure of ? b .

Cavaliers principle states that two solids with equal heights and cross-sectional volumes at every level have equal areas.