Help needed finding an equation.

I know this is probably elementary for the users of this site, but I have a problem that I am struggling to even find an equation for, let alone the solution. Here is the problem:

*You have $135,245,210. How many items can you purchase if they cost $221,400 and their price increases by $1800 with each item purchased?*

It's been quite some time since I've done any Algebra, and I cannot even come up with the equation to find the solution. So any help would be much appreciated. Thanks!