Why should we tell you the answer when you've already given one? Are you looking for help, or something else?
On what grounds do you claim that only a genius can solve it? What data do you have? (There is far too much of this sort of claim on social media, so I just ignore it.)
In fact, it's extremely easy, in my opinion. It takes far less work than you show; and you have at least one typo (1/2 where you surely meant 1/3).
But here's the solution: The large cone is similar to the smaller one, and 3 times the height; so it has 3^3 = 27 times the volume. Their difference (the frustum) is therefore 27 - 1 = 26 times the volume of the large one. No formulas, no writing needed.