Amazon gives non-Prime members free shipping at $35 or more of eligible items. Instead of simply letting users get the product with free shipping, they’ve added a discount that prices it exactly one cent below the $35 limit, while only subsidizing the price with $3.38, which is about half of what they’ll then charge you for shipping.
Profit is revenue - cost of goods.
If you make a widget and it costs you $100 to make, and you sell it for $110, you have $10 profit. Then you have all the other expenses that it takes to run a business, lets say that’s $200.
Your revenue is $110
You profit is $10
Additional Expenses: $200
You NET profit (AKA Net Income) is $-90