A rower can row 7 km/h in still water. When the river is running at 2 km/h, it takes the rower 1 hour to row to Big Rock and back. How many kilometers is it to Big Rock?
Choose the most appropriate option:
A) 2.92
B) 3.04
C) 3.12
D) 3.21
E) 3.35
Let x be the distance to Big Rock.   time = x/5 + x/9 = 1   x = 45/14 = 3.21 km   The answer is 3.21.
<result>D</result>
A rower can row 7 km/h in still water. When the river is running at 2 km/h, it takes the rower 1 hour to row to Big Rock and back. How many kilometers is it to Big Rock?