Question

If a 25 cm long candle burns for 45 min how long will a 30 cm candle burn

Answer 1

25cm - 45 min
30 cm - X min

(30*45)/25 = X 
Here X=54 So it will burn for 1 Hr min That is 54 min 

Answer 2

25cm long candle burns in 45min
then, 30cm long candle burns in 45/25*30=54min