A rower can row 5 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 correct choice from the following
A) 1.5 B) 1.8 C) 2.1 D) 2.4 E) 2.7

Rationale: "let x be the distance to big rock . time = x / 3 + x / 7 = 1 x = 21 / 10 = 2.1 km the answer is c ."
Answer: C