If I'm getting this right... there's 2 candles and matches, and one test that takes an hour and a half to do. Each candle burns for an hour, so you light one, take the test and when that candle gets low you light the second one. Is this a trick question?
Light the first candle, do the exam, then light the second when the first is used up, then simply blow it out when you're done. Although presuming the room is dark you could probably use it to light your way out as well, thus proving doubly useful