I know only a small section of the data can be seen but I just need help figuring out what formulas I should use so it doesn't matter if the answer only takes into account the rows shown in the photo. I'll just adjust the formula so that it contains every row

\begin{tabular}{|l|r|r|r|r|r|} \hline 6 & Year & Total Outstanding Receivables & Percent of sales on account written off & \multicolumn{2}{|c|}{ Percent of outstanding receivables written off by receivale age group } \\ \hline 7 & & & & \\ \hline 8 & 2013 & 5 & & \\ \hline 9 & 21,450,076 & & \\ \hline 10 & 2014 & & \\ \hline 11 & 2015 & & \\ \hline 12 & 2016 & & \\ \hline 3 & 2017 & & \\ \hline 4 & & & \\ \hline \end{tabular}