took just 40 second by backsolving...
total distance 400 miles..
start with B , let carB speed = 30
time taken = 400/30=13.33
we know car A speed with 10 greater than B so A = 40
Time taken = 400/40=10 ( time difference greater than 2 hour wrong)
try C , Car B speed 40 , time taken 10 hours
then Car A speed 50 , time taken 8 hours ...which is 2 hours less....
so ...ans C
The time it took car A to travel 400 miles was 2 hours less than the time it took car B to travel the same distance. If car Aâ€™s average speed was 10 miles per hour greater than that of car B, what was car Bâ€™s average speed, in miles per hour?