What is a way to write - 85 divided by 15 as a word problem?

If something is negative then it is decreasing. We can express this in terms of velocity per second.

"A car is traveling backwards. What is its velocity if it travels 85 miles in 15 seconds"

This is the easiest word problem I can think of. (When a car travels backwards it has a negative velocity but a positive speed).

The balance in my bank account went down $85 in 15 days. How much did it change per day. Use a positive number to represent a gain of money and a negative number to represent a loss of money.

The change in balance is a loss of money, so the change is - 85.

The change of - 85 occurred in 15 days, so the average change per day is

-85/15