Problem $2$:

Crash the network below to its minimum duration at

$\backslash$table$[[$Activity$,\backslash$table$[[$Total$],[$Cost$]],\backslash$table$[[$Minimum$],[$duration$]],\backslash$table$[[$Crash cost$],[$per day$]],\backslash$table$[[$Activity$],[$Total$],[$Cost$]],\backslash$table$[[$Minimum$],[$duration$]],\backslash$table$[[$Crash cost$],[$per day$]],],[$A$,$$$5,000,1,--,E,$$$18,000,5,$$$2,900$