In this case, "the number of hamburgers sold" would be the independent variable, as it is the factor that is being manipulated or controlled in order to observe its effect on another variable.
On the other hand, "the dollar amount of sales taken in" would be the dependent variable, as it is the variable being measured or observed, and its value depends on the number of hamburgers sold. The sales amount is affected by the number of hamburgers sold, which is the independent variable.