What was the challenge?
1. Burn both the ends of 1st String and 1 end of other string.
2. After 30 minutes, 1st string will be Burnt out and half of the other string will be burnt out.So far we have counted 30 minutes.
3. Now burn the other end of 2nd end. It will take 15 minute to burnt out totally. This way, we have counted 30 + 15 = 45 minutes using 2 strings.