Composite figures are two or more figures combined. when finding the surface area , you cannot simply find the separate surface area and add them. what face(s) do you have to exclude from the total surface are? ?

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.