$225
Step-by-step explanation:
The user went over the 15 GB limit this time, so the overage charge will apply.
The overage charge is $10 per GB that's over this limit. So, we need to find the total amount that gets charged.
This person used 20 GB. 20 GB - 15GB = 5 GB too much.
5 x 10 = $50 for the overage fee.
The problem already tells us that the charge for 15GB is $175. So let's just add the overage fee to that. $175 + $50 = $225