Correct option - C
Let's analyse all the options
1. x is greater than or equal to 20.This isn't possible as if x = 20 ,hats would come in negative
2. All real numbers is of course not possible.
3. This makes sense, because the amount will be not in negative and 300 hats has to be sold first.
4.Not possible.As 'x' can't be less than 0 or greater than 500
Hope This Helps You!