Stadium Construction Project Problem: What is the project duration?

ACTIVITY IMMEDIATE PREDECESSOR DURATION $($days$)$

$\backslash$table$[[$A$,-,1],[$B$,$A$,4],[$C$,$A$,3],[$D$,$A$,7],[$E$,$B$,6],[$F$,$C$,$D$,2],[$G$,$E$,$F$,7],[$H$,$D$,9],[$I$,$G$,$H$,4],[,,]]$