A construction project is broken down into the following $8$ activities:

$\backslash$table$[[$Activity$,$Immediate predecessor,Time $($days$)],[$A$,-,2],[$B$,$A$,5],[$C$,$A$,4],[$D$,$B$,1],[$E$,$C$,$D$,6],[$F$,$D$,3],[$G$,$F$,2],[$H$,$E$,$G$,4]]$

$($c$)$ What is the slack of activity C$?$