Refer to Problem $26$ and Figure $13\mathrm{.}20.$ a$.$ For Network $($a$),$ suppose after $7$ weeks, activities A$,$ B$,$ and E have been completed, D is $50$ percent completed, and C is $80$ percent completed. What is the revised early completion date for the project? b$.$ For Network $($b$),$ suppose after $25$ weeks, activities A$,$ B$,$ C$,$ F$,$ E$,$ G$,$ and I have been completed, and D and H are ready to begin in week $26.$