Explain simply why (C) is the correct answer to: The speed of a boat in upstream is 100 kmph and the speed of the boat downstream is 120 kmph. Find the speed of the boat in still water and the speed of the stream?
Options:
(A) 70, 10 kmph
(B) 35, 27 kmph
(C) 110, 10 kmph
(D) 45, 55 kmph
(E) 45, 65 kmph. Explanation:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
Speed of the boat in still water = (100+120)/2 = 110 kmph. Speed of the stream = (120-100)/2 = 10 kmph