Justin drove 7 hours yesterday.
Since Justin drove two hours today at an average speed of 56 miles per hour, that would mean that he had driven 112 miles today, 56 x 2. If you subtract that from 504, you would get 392, which is how many miles he's driven yesterday. To get how long it took, you would divide 392 by 56 which is how many miles he drives per hour, and you would get 7.
