Solution: When 1H is chasing, B has the fastest speed, set to X 1, and when 1.25H is chasing, B has the slowest speed, set to X2.

X 1=(2+ 1)*5

X 1= 15

1.25*X2=( 1.25+2)*5

X2= 13

So the range is within 13~ 15KM.