Another Quadratic Equation

I buy a number of cheap calculators for a total of $240, mark each of them up by $2 and sell all but four of them for a total of $240. How many calculators did I buy?

Okay, so this is what I have done so far:

Let y represent the cost per calculator, and let x represent the number of calculator.

Therefore, xy = 240

And with the addition of the $2.00, minus the four pencils:

(x-4)(y+2) = 240

xy+2x-4y-8 = 240

and now im stumped. what do i do?

please explain + thanks in advance!