Average speed of the first car= 15 miles/hr
Average speed of the second car= 30 miles/hr
Explanations:
distance= d= 90 miles
Time= 2 hrs
let speed of first cyclist= v
speed of second cyclist= 2v
relative speed = v + 2v= 3v
using relative speed= Total distance/Total time
3v= 90/2
3 v=45
v=15 miles/hr
so speed of first cyclist= 15 miles/hr
speed of second cyclist= 2 (15)= 30 miles/hr