Runtime Calculation Sort-Algortihm
Do not even mention big-O here because that is for asymptotic behaviour and f(1000) doesn’t give you the slightest clue what f(2000000) would be. 

You are given that the runtime is f(n) = c x g(n) for three different functions c. Given the value of c x g(1000) for the first function g, you calculate c. Then you substitute c and n for all the cases.