Three activities are candidates for crashing on a project network for a large computer installation $($all are, of course, critical$).$ Activity details are in the following table:

$\backslash$table$[[$Activity$,\backslash$table$[[$Normal$],[$Time $($days$)]],\backslash$table$[[$Crash$],[$Time $($days$)]],\backslash$table$[[$Normal$],[$Cost$]],\backslash$table$[[$Total Cost$],[$with$],[$Crashing$]],$Immediate Predecessor$($s$)],[$A$,7,6,$$$5,000,$$$5,600,-],[$B$,4,2,$$$1,200,$$$3,100,$A$],[$C$,11,9,$$$4,600,$$$6,600,$B$]]$

a$)$ Activity that should be crashed first to reduce the project duration by $1$ day is

b$)$ Activity that should be crashed next to reduce the project duration by one additional day is

c$)$ Total cost of crashing the project by $2$ days $=$$$3100.($Enter your response as an integer.$)$