Question 520854
Effective Speed = 100 + 80 = 180 kmph
Distance apart = 100 km
Time = Distance / Speed
Time = 100 / 180
Time = 0.556 hour 


After 0.556 hour they will be (approximately)100 kilometers apart.



Check
=====
Mr. Anders will cover = Speed * time = 100*0.556= 55.60 km
Mr. Rich will cover = Speed * time = 80 * 0.556 = 44.48 km
After 0.556 hour they will be = 100.08 miles apart.