Your algorithm for rendering a scene of your game results in a maximum refresh rate of 25 frames/s, for a screen (frame) of 1000x1000 pixels, barely within your acceptable range. You have estimated that your algorithm is O(N^3) (worst case tight bound) to refresh your screen consisting of N pixels. What will the approximate refresh rate in frames/s be if the screen size is increased to 2000x2000 pixels? You may express the result in fractional form. Assume that log21000 = 10. 

The answer is 24/64 fps. I'm not sure how..