CVS is attempting to quantify the underlying "PSI Business Case in Numbers": if the effort were to be produce results (a component of upstream thinking)the potential impact of PSI on revenues via the estimated defection rates could be significant. Refer to the below quote as the starting point to read, absorb and to estimate the impact via 3a and 3b. [Answer below questions.] To do this: -You need to distinguish the number of customers versus number of scripts. -The case provides [what-if] guidelines for minimum and maximum reduction of defections, which you can use to estimate the contributions of PSI. [More hints are provided below.]