A boat covers a certain distance downstream in 1 hour, while it comes back in 1.30 hours. If the speed of the stream be 3 kmph, what is the speed of the boat in still water?	Select the correct option: A) 10 B) 13 C) 11 D) 08 E) 15

Rationale: "let the speed of the water in still water = x given that speed of the stream = 3 kmph speed downstream = ( x + 3 ) kmph speed upstream = ( x − 3 ) kmph he travels a certain distance downstream in 1 hour and come back in 1 1 ⁄ 2 hour . i . e . , distance travelled downstream in 1 hour = distance travelled upstream in 1 1 ⁄ 2 hour since distance = speed × time , we have ( x + 3 ) × 1 = ( x − 3 ) 3 / 2 ⇒ 2 ( x + 3 ) = 3 ( x − 3 ) ⇒ 2 x + 6 = 3 x − 9 ⇒ x = 6 + 9 = 15 kmph answer is e ."
Answer: E