Let x = the distance between A and B.
Day 1: Traveled x/3 | Remaining = (2/3)x
Day 2: Traveled (2/5)(2/3)x = (4/15)x | Remaining = x - x/3 + (4/15)x => x - (5/15)x + (4/15)x = (15/15)x - (9/15)x = (6/15)x
Day 3: Traveled 144
Use this to solve for x: 144 = (6/15)x => x =360
Day 1: 360/3 = 120