Assuming the speed of bus starting from B is V , then
the speed for bus from A =V+10
Thus V1 = Speed of A =V+10
V2 = Speed of B =V
If x is the distance between the cities
V1 = V+10 =x/3.5
V2 = V = (x/6) /3.5
Solving these two equations x = 420 mi
V =(420/3.5) -10
V= (385/3.5)=110 mi/hr
V1 = 110+10
=120mi/hr
V 2= 110mi/hr
Distance between the cities = 420miles
and speeds of buses are 120mi/hr and 110mi/hr