Atwelve cm candle and an 18 cm candle are lit at 6pm. the 12 cm candle burns 0.5cm every hour. the 18cm candle burns 2 cm every hour. at what time will the two candles be the same height?

The size of the candle 12cm will be reduced as follows:
12-0.5x (x are hours), an the size of the candle 18cm will be reduced as follows: 18-2x, so if you want to find at what time both will be the same height only match the two equations: 12-0.5x=18-2x and solvr for x.
-0.5x+2x=18-12
1.5x=6
x=6/1.5=4 this means 4 hours
If you lit both candles at 6pm then at 10pm they will be the same height
(adittional info: the height will be 10inches) 

Bi’m pretty sure hope it works