✪ Choose the correct option.
Abhinandan starts in a car from Amritsar towards Bangalore. After some time he realises that he will cover only 80% of the distance in the scheduled time and he therefore hastened at thrice his speed and thus managed to reach Bangalore exactly on time. Find the time after which Abhinandan changed his speed, given that he could have been late by 4 hours if he had not made the changes.