What's the project variance and the standard deviation? Please show work.

\begin{tabular}{|l|l|l|l|l|} \hline Activity & a & m & b & Immediate Predecessor \\ \hline A & 1 & 2 & 3 & \\ \hline B & 2 & 3 & 4 & \\ \hline C & 4 & 5 & 6 & A \\ \hline D & 8 & 9 & 10 & B \\ \hline E & 2 & 5 & 8 & C,D \\ \hline F & 4 & 5 & 6 & B \\ \hline G & 1 & 2 & 3 & E \\ \hline \end{tabular}