In this scenario, the independent variable is \( p \), the number of people who attend the screening, and the dependent variable is \( s \), the number of seats needed.
The reasoning behind this is that the number of seats (\( s \)) depends on the number of attendees (\( p \)). As the number of people attending increases, the number of seats that need to be set up will also increase. Therefore, the attendance \( p \) is the independent variable, and the required seats \( s \) is the dependent variable.