Please complete the partially filled in network diagram below.

\begin{tabular}{|l|r|r|} \hline 15 & & 30 \\ \hlineF & 15 \\ \hline & & \\ \hline \end{tabular} \begin{tabular}{|l|l|c|} \hline ES & TF & EF \\ \hline A & \multicolumn{2}{|c|}{t} \\ \hline LS & FF & LF \\ \hline \end{tabular} \begin{tabular}{|l|r|r|} \hline 15 & & 30 \\ \hlineF & 15 \\ \hline & & \\ \hline \end{tabular} \begin{tabular}{|l|l|c|} \hline ES & TF & EF \\ \hline A & \multicolumn{2}{|c|}{t} \\ \hline LS & FF & LF \\ \hline \end{tabular}