The faster car would be traveling at 60 miles per hour and the slower car would be traveling at 40 miles per hour.
300÷3=100 so once you find how long they travel per hour. you need to divided they into equal parts. than you need them to be 20 apart(one is traveling 20 mi. faster than the other) if you give 10 to the other it leaves you with 60 and 40. Hope this helps and I didn't confuse you!