If they start from two places at the same time and turn their backs on each other, (if they can only meet in the same direction, they will only pursue it when they come back)
When they meet within 1.5 hours, the sum of their velocities is 1÷ 1.5=2/3.
The speed ratio is 5: 6.
So the speed of two people is
A: 2/3×5/(5+6)= 10/33.
B: 2/3×6/(5+6)=4/ 1 1。
The speed difference between them is 4/11-10/33 = 2/33.
When two people walk with their backs to each other, the distance difference is 1
So the time for B to catch up with A is 1÷2/33= 16.5 hours.