The speed of a boat in still water is 18 kmph. What is the speed of the stream if the boat can cover 48 km downstream or 32 km upstream in the same time? Choose one.
A) 4 kmph	B) 5 kmph	C) 6 kmph	D) 7 kmph	E) 8 kmph

Rationale: "x = the speed of the stream ( 18 + x ) / ( 18 - x ) = 2 / 1 18 + x = 36 - 2 x 3 x = 18 x = 6 km / hour if the speed of the stream is 6 km / hour , then the ' downstream ' speed of the boat is 18 + 6 = 24 km / hour and the ' upstream ' speed of the boat is 18 - 6 = 12 km / hour . in that way , if the boat traveled for 2 hours , it would travel 2 x 24 = 48 km downstream and 2 x 12 = 24 km / hour upstream . answer : c"
Answer: C