The surplus is 1760/2=880.
B keep it at 1760-720= 1040.
When the speed ratio of Party A and Party B becomes 9: 1 1, let the speed of Party A be 9m/s and that of Party B be1/m/s,
Then: A left 880/9 = 97.78.
B walked the whole journey of1040/11= 94.5445.
The time unit difference is 97.77778-94.5454=-3.23233.
So b arrived first;
(Hope to adopt)