Because it takes 4 hours for a short candle and 5 hours for a long candle, the short candle burns 1/4 and the long candle burns 1/5 every hour, which is set to x hours.

There are:

1-x/5=3( 1-x/4), and the solution is x=40/ 1 1.

A: Two candles have been lit for 40/ 1 1 minute.