That awesome moment when you're absolutely sure you're going to get the "incorrect" ding, but turns out you did it right. :)
what about "vuole dimostrare che è possibile da fare"? no solution?
"Vuole dimostrare che è possibile farlo" would be better than your version. I know, prepositions are so difficult. I don't even want to know how many mistakes I make in English ones. :D