After two hours, the first car has traveled (2 x 60) = 120 miles.
That's the gap that the second car has to close.
The second car closes the gap of 120 miles in 6-2/3 hours.
He must have exceeded the first car's speed by (120/6-2/3) mph.
6-2/3 = 20/3
120 divided by 20/3 = 120 x 3/20 = 360/20 = 18 mph
The second car exceeded the first car's speed by 18 mph,
so he had to be traveling (60 + 18) = 78 mph to catch up.
Check:
In 6-2/3 hours . . .
The first car covers (60 x 20/3) = 400 miles.
The second car covers (78 x 20/3) = 520 miles.
This is the same distance as the first car PLUS the 120
that he was behind when he started out.
yay !
