Search up heating curve chemistry: it should look somewhat like that lol :). But, the last interval should have a small slope, the middle interval a big slope, and the first interval: a medium slope.
To set the equation,we can first find how much price would be raised within a year:
=500×(1+7%)
=500×1.07
As the years go by the increase would accumulate,and the equation would be:

Hope it helps!