Over 7 hours a balance changes by a total of -56 units, by the same amount in every hour. What is the change per hour?

توضیح

Sharing a total drop of 56 equally between 7 hours gives a drop of 8 in each of them, and a drop is recorded below zero just as the total was. Answering 8 divides the sizes correctly but describes an hourly gain, and joining the 56 to the 7 by addition or subtraction ignores the sharing altogether.