What type of additional charge can guests add to their drinks for $3?

The correct response is based on the option of adding extra liquor to drinks for an additional charge of $3. This practice is common in many establishments, including bars and restaurants, where customers may choose to enhance their beverage experience by increasing the quantity of alcohol in their drink. This option allows for greater customization of cocktails and other beverages, appealing to patrons who may desire a stronger drink or simply wish to enjoy more of their favored liquor.

While flavored syrup, extra ice, and premium mixers can also enhance drinks, they typically do not carry an additional charge of the same nature. Flavored syrup may be offered complimentary as part of the customization process, extra ice generally does not require an extra fee, and premium mixers might be a higher base cost rather than a straightforward addition for a nominal fee. Thus, extra liquor stands out as the ideal answer when considering additional charges for enhancing a drink.