Please if you can explain how you calculate each one that would help me tremendously

\begin{tabular}{|l|r|r|r|r|r|r|r|r|r|} \hline Weeks & & 1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 \\ \hline Gross Requirement & & 20 & 0 & 60 & 0 & 100 & 80 & 0 & 60 \\ \hline Scheduled Receipts & & & 100 & & & & & & \\ \hline Projected On-Hand & 80 & & & & & & & & \\ \hline Planned Receipts & & & & & & & & & \\ \hline Planned Order Release & & & & & & & & & \\ \hline \end{tabular}