MAC$\_1=16-$ E$\_1$

MAC$\_2=24-2$E$\_2,$

and assume marginal external damages $($MED$)$ from the aggregate emissions of both firms $($E$\_$Agg $=$ E$\_1+$ E$\_2)$ is:

MED $=2$E$\_$Agg.

To achieve the socially efficient level of aggregate emissions $($E$*\_$Agg$),$ the government institutes a cap and trade policy and sets the permit cap equal to $\_\_\_\_.$