Given a simple project illustrated in the following table

Activity Immediate Predecessors Time (weeks) 1 - 2 2 1 3 3 2 2 4 2 5 5 3, 4 4

The required project completion time is 15. Assume that "Activity 1" actually finished at 3 weeks, and "Activity 2" actually finished at 7 weeks. Given the actual project progress, what is the LF (lastest time) of "Activity 4"?

\begin{tabular}{|l|l|l|} \hline Activity & \begin{tabular}{l} Immediate \\ Predecessors \end{tabular} & \begin{tabular}{l} Time \\ (weeks) \end{tabular} \\ \hline 1 & - & 2 \\ \hline 2 & 1 & 3 \\ \hline 3 & 2 & 2 \\ \hline 4 & 2 & 5 \\ \hline 5 & 3,4 & 4 \\ \hline \end{tabular}