Which calculation is essential for determining how long a chemical has been applied in a specific area?

To determine how long a chemical has been applied in a specific area, the most directly relevant piece of information is the duration of application, which is effectively captured by the measurement of minutes applied. This measurement gives a precise timeline for how long the chemical exposure has occurred, which is crucial for understanding its potential effects on the aquatic environment and the efficacy of control measures.

Other options may be related to various environmental variables or physical characteristics of the application site, such as flow rates or areas, but they do not directly provide the essential information regarding the application time. Knowing the duration allows for an assessment of both the potential impact on non-target organisms and the timing for subsequent management interventions.