Answer:
$0.05 per day
Explanation:
So we know that the initial late fee would be $0.50. For every additional day, the fee increases by $0.05. The rate of change would be the rate at which the cost of the fee changes.
Note, the initial value does not affect the rate of change.
The initial late fee of $0.50 would not affect the rate of change, so we can ignore that piece of information.
Since the fee increases by $0.05 daily, $0.05 per day would be the rate of change.
I hope this helps.