Answer:
3 or 4 I think
Explanation:
I think this because if u find the red candles unit rate it's 9 and 9×4 is 36 but the thing is the other one is 12 12×4 is 48 but then if u do 12×3 it's 36. The rest don't work so 3 or 4 hours. But if someone else has a different answers do not put mines because I have no clue but I think it's that because of that reason.