Kanon's Riddle: Hint

[prof]

This is just to buy time until Shannon can think of a question, so forgive me.
Th-Thank you! I've thought of a question...!
Understood. Now then, Eva and Ange. I'll give you a hint. Copper is 29, silver is 47, and gold is 79. That's the hint.
That's just what you said in the question! That's not a hint!
Copper is 29? Silver is 47? ...Oh, so that's it!
Huh? You got it?! I get it too! Platinum is better than gold, so the prize must be more than 79 gold coins!
That's wrong. With these rules, the platinum prize is probably worth less than the gold prize. Isn't that right?
It is as you say. It seem you've already found the answer.
This puzzle is impossible for Ange. You'd need to have gone to middle school at the very least. I'll answer! Is that alright, Ange?
S-Sure. I'll leave it to you!