Products Sold Until Investment Caps

I've been trying to make an equation for the total amount of copies that a product needs to sell until it reaches a certain limit. Specifically, I have two products that sell for 5.80 and 4.30 respectively. My goal is to find out how many products need to be sold before the investor of the product reaches the limit, $25,000.00, on their investment at 18%.

I then need another equation to compliment the first, or maybe a combination of the two, that takes all proceeds and turns anything excess of the $25,000.00 into a 3% investment.

Any help with this would be greatly appreciated, I've been working on trying to figure this out for 12 hours now.