Question 251944
As cute as this problem is, there is not enough information, since you didn't tell us anything about the town! Nor where the colors were heading nor where they are now.
If all the colors were heading toward town.
rate * time=distance
red
50*(t)=200
t = 4
yellow
40*(t)=30
t=0.75
blue
75*(t-15)=50
t=15.6667
Green 
60*(t-15)=25
t=15.4167
white
30*(t-30)=10
t=30.3333

The lowest t's arrive first