Q$4.(05$ points$)$ The diagram below shows the activities on the nodes, and the table shows the normal time and crash time $($in days$)$ and cost for each activity. Start E Activity Normal Time Crash Time Cost per day to crash $66$ B $108$ $$10054$ $$300$ D $41$ $$700$ E $97$ $$500$ F $2$ S$650$ a$)$ Which activity should be crashed to reduce the project completion time by one day? b$)$ Which activity should be crashed to reduce the project completion by $2$ days?