Question 903056
The bike from b had a(n) 0 hour headstart
The distance traveled in those 0 hours is 0 miles
The distance to go 48 miles
d=r*t+R*t
48=15*t+25*t
48=40*t
t=1.2 hours
The total time for bike from b to meet the bike from a is 1.2 hours
d=R*t
d=25*1.2
d=30.0+0
d=30.0 miles from b at 25 mph
d=r*t
d=15*1.2
d=18.0 miles from  a at 15 mph
For out purpose it doesn't matter which direction Spot is running.
The cyclist are moving for 1.2 hours and so is Spot.
1.2*35=42 Spot has run 42 miles 
I don't think greyhounds have that stamina!