According to the PMBOK® Guide and the Standard for Project Management, specifically within the Develop Schedule process using the Critical Path Method (CPM), the relationship between the forward pass and the backward pass determines the amount of Total Float.

As per PMI standards, Total Float is the amount of time that a schedule activity can be delayed or extended from its early start date without delaying the project finish date or violating a schedule constraint. The calculation for Total Float is:

$$\text{Total Float} = \text{Late Finish (LF)} - \text{Early Finish (EF)}$$

or

$$\text{Total Float} = \text{Late Start (LS)} - \text{Early Start (ES)}$$

In the scenario described:

Forward Pass: Calculates the Early Finish (EF) date.

Backward Pass: Starts from a Schedule Constraint (the required completion date).

The Condition: The constraint (LF) is later (further in the future) than the calculated EF.

Because the Late Finish is greater than the Early Finish, the result of the subtraction is a Positive value. This indicates that the project or activity has " extra " time or a buffer before it would impact the mandatory constraint.

The other options are incorrect based on the following PMI scheduling logic:

Negative: This occurs when a schedule constraint is earlier than the calculated early finish date ($LF < EF$), indicating the project is already behind the required deadline.

Zero: This occurs when the late finish is equal to the early finish ($LF = EF$), which is typical for activities on the Critical Path.

Free: This is the amount of time an activity can be delayed without delaying the Early Start of any successor activity. It is a relationship between activities, whereas the question describes a relationship between a pass calculation and a project-level constraint.

As per the PMI Lexicon of Project Management Terms, understanding positive float is essential for resource leveling, as it identifies which activities have flexibility to be shifted without jeopardizing the final deadline.