Diwali

Diwali is the festival of lights. Celebrations are filled with fireworks, diyas, and candles, creating stunning designs. You are designing a rangoli and want to use three candles of different sizes. You know that each size of candle has a different burning time, the small ones will burn for exactly 1 hour, medium for exactly 3 hours, and the large for exactly 4 hours, but they do not burn at constant rates.

You could measure 5 hours exactly by first burning the 1 hour candle, and then burning the 4 hour candle as soon as the 1 hour candle finishes. However, you could not burn the 4 hour candle halfway to measure 2 hours, because you would not know where halfway is, since the candle doesn’t burn at a constant rate.

Of the options below, which is the longest length of time from now that you cannot measure exactly?