What is necessary to accurately calculate the number of ingredients for shots?

To accurately calculate the number of ingredients for shots, it's essential to consider the number of shots required for a standard serving, which is often based on a typical pour size. In this case, multiplying the number of shots by four aligns with the common practice of using 1 ounce of liquor per shot and the requirement for a standard four-ounce mixing portion. This method ensures that when preparing cocktails or shots, a bartender will have the right amount of each ingredient necessary for the specified number of servings.

The other options would not yield the needed quantity for a standard serving. Dividing by four, adding four, or subtracting four do not correspond to the standard measurements used in bartending and would likely result in either insufficient or excessive amounts of ingredients, leading to poorly made drinks. Understanding the correct measurement is crucial for consistency and quality in drink preparation.