A bank customer borrowed 10,000 dollars, but received y dollars less than this due to discounting. If there was a separate 25 dollars service charge, then, in terms of y, the service charge was what fraction of the amount that the customer received?

My Work:

The amount of money the customer received was (10,000 - y) dollars. I do not understand how to create a fraction from the given information. The answer is 25/(10,000 - y). Why is this answer correct in terms of the service charge as a fraction?