In a stream running at 2 Kmph, a motor boat goes 10 Km upstream and back again to the starting point in 55 minutes. Find the speed of motor boat in still water?
Choose the correct choice from the following answers:
A) 11	B) 15	C) 22	D) 18	E) 25

Rationale: "let the speed of motor boat instill water be x kmph then , speed in downstream = ( x + 2 ) km and . speed in upstream = ( x - 2 ) kmph time taken to row 10 km & back = ( 10 / x + 2,10 / x - 2 ) 10 / x + 2 + 10 / x - 2 = 55 / 60 11 x 2 - 240 x - 44 = 0 ( x - 22 ) ( 11 x + 2 ) = 0 x = 22 or x = - 2 / 11 then x = 22 kmph answer is c ."
Answer: C