Stadium Construction Project Problem: What is the project duration?

$\backslash$table$[[$ACTIVITY$,$MMEDIATE PREDECESSOR,DURATION $($days$)],[$A$,$A$,1],[$B$,$A$,4],[$C$,$A$,3],[$D$,$B$,7],[$E$,$C$,$D$,6],[$F$,$E$,$F$,2],[$G$,$D$,7$ A$],[$H$,,9]]$

$23$ days

$24$ days

$20$ days

$22$ days

$21$ days