Check the picture below.
now, to get how much is the area of the tiled section, we simply get the area of the whole pool, 53x26, which includes the tiles, and then subtract the area without the tile, the rectangle in the middle, and what's leftover, is the area of the tiled area.

Speed = Distance ÷ time
Speed upstream = 84 ÷ 7 = 12 km/h
Speed downstream = 84 ÷ 3 = 28 km/h
Speed in still water = 1/2(28 + 12) = 20 km/h
Answer: 20 km/h
Im late but i had this test its car A < rate of car B hope it helps