Consider a product w/ 5 customers willing to pay $6, $5, $4, $3, and $2, respectively, which has constant marginal cost of $2.50/unit. If you are a monopolist and can identify a group of customers willing to pay less than the standard monopoly price but more than marginal cost for the product, you can maximize profits by offering prices of $5 to high-value customers and...____ to low-value customers.

I see from a previously answered question the answer is $4, but why not $3? How did they get to that answer?