On a shopping trip, Sofia decided to buy a light blue coat that had a price tag of $79.95. When she brought the coat to the store's sales clerk, Sofia was told that the coat was on sale, and she would pay 20 percent less than the price on the tag. After the discount was applied, Sofia paid $63.96, $15.99 less than the original price. Was the value of Sofia's consumer surplus from this purchase $79.95? $63.96? $15.99? Or some other amount? Briefly explain.