 Solution

Expected death counts are the number of users multiplied by the death risk per user, with matching time windows and definitions. Relative to the MDMA benchmark, the proposed use prevalence contributes a multiplier of $0.6$ and the per-user fatality risk contributes a multiplier of $0.5$. HenceThis assumes comparable user exposure durations and recording of single-drug deaths. Population death counts alone would not identify a per-user risk ratio without the prevalence denominator.