There are several information's of immense importance already given in the question. Based on these information's the answer can be easily deduced. Let us now focus on the problem in hand.
Amount paid by the center per kilogram of aluminium = $0.002 The equation is t = 0.002n dollars
50-x^2=0 Move the x^2 to the other side x^2=50 Now take the square root of both sides x=+_(50)^1/2 (^1/2 means square root)(+_ is plus or minus. Sorry XD) Now simplify the square root X=+_5(2)^1/2 Voila. The answer is C
