Maximizing Notebooks within Cost Constraints

Consider the function described by the linear equation $$y = 3x - 2$$. This function represents the cost (in dollars) of purchasing $$x$$ notebooks. Additionally, a store offers a promotional discount on a certain number of notebooks. If customers can buy $$n$$ notebooks, with the first 5 costing the regular price and any additional notebooks after the 5th priced at a discounted rate of $$2$$ dollars each, how many notebooks can a customer buy such that their total cost does not exceed $$20$$?