The following table shows information related to the major activities of certain project.

$\backslash$table$[[$Activity$,\backslash$table$[[$Immediate$],[$Predecessor$]],\backslash$table$[[$Normal Activity$],[$Time $($Week$)]],\backslash$table$[[$Crash Activity$],[$Time $($Week$)]],\backslash$table$[[$Crashing Cost$],[$Per week $($$$)]]],[$A$,-------,10,10,------],[$B$,-------,08,07,8,000],[$C$,$A$,12,12,------],[$D$,$B$,06,05,12,000],[$E$,$C$,$ D$,05,05,------],[$F$,$D$,14,11,10,000],[$G$,$F$,16,14,16,000],[$H$,$E$,$ F$,17,12,14,000]]$

If the project completion time is shortened by $3$ weeks, determine:

a$.$ The activities that must be crashed and the corresponding number of crashing weeks.

b$.$ the total crashing cost.