Rate x time = distance (Or amount burned)
rate1 = 1candle/6hr= 1/6
rate 2 = 1 candle/ 4 hours = 1/4
amount remaining after x hours = 1 candle - rate * x
1- 1/6 *x = 2 (1- 1/4 * x)
1- 1/6 x = 2 - 1/2 x
1= 2/6 x
x = 3 hours
( I couldn't find the other posted answer)
3 hrs x 1/6 = 1/2 Burned = 1/2 left
3 hrs x1/4 = 3/4 Burned = 1/4 left