Similar way here, given 0000, 1111, 2222, 3333, 5555, 6666, 7777, 9999, we know the value of each number except for 4 and 8, disregard 4 (not in any value), sub those values in to any slot with an 8, and you get the answer.

If the alternative to overthinking would be staring at this looking for a pattern until you realize it is the number of loops, then that is not something I am interested in :)