$$ \text{Revenue Loss} = \text{Number of Pirated Copies} \times \text{Revenue per Copy} $$
However, this is a vast oversimplification of a complex issue and is not directly related to the topic's core but illustrates how one might approach quantifying impacts with mathematical expressions.
If one were to model the impact of piracy on film revenue, a simple equation could be:
In a mathematical context unrelated to the direct analysis but following your requested format for mathematical expressions: