158679

Complete text that accompanies her diagram:
If each candle lasted two years, they would need 36 candles altogether.

The way I worked it out is I drew the candles so that the ones with bits on the top are the ones that have already been used for one year and the ones that don't have bits on the top have just been bought. The way I did it was I looked at the newly-bought ones and changed them into the ones that have already been used (for the next year). Next, I counted how many used ones there are and then added more to get enough for how old he is, eg. for the sixth birthday, the three candles from the previous year can be used so he needs three new ones.