The problem statement says that Amit takes a total time of 6 hours 45 minutes to walk one way and drive back. If he drives both ways, he will take 2 hours less, so driving one way takes (6 hours 45 minutes - 2 hours =) 4 hours 45 minutes. Now, since it takes 4 hours 45 minutes to drive one way and 6 hours 45 minutes to walk one way and drive back, the difference (6 hours 45 minutes - 4 hours 45 minutes =) 2 hours is the extra time taken to walk instead of driving one way. So, if he walks both ways, he would take (4hours 45 minutes to drive one way + 2 hours walking extra for one way) x 2 = 8 hours 45 minutes. So, option 4 is correct.