Table with box inside - latex

Question

How to code this kind of table? The code for the table is easy for me but I don't know how to put a box in the upper right in every column. Thank you.

Answer 1

I found a way to add a box in the upper right corner, by adding additional columns (one left and one right for symmetry reasons) and rows to the table.
This is my solution, though they are propably more elegant ways to achive this:
\documentclass{article}
\usepackage{array}
\newcolumntype{P}[1]{>{\centering\arraybackslash}p{#1}}
\begin{document}
\begin{table}
\centering
\begin{tabular}{|c P{15mm} c|c P{15mm}c|cP{15mm}c|cP{15mm}c|c P{15mm}c|}
\hline
& & & & & & & & & & & & & & \\
& & & & A & & & B & & & C & & & Capacity & \\
& & & & & & & & & &
& & & & \\
\hline
& & & & & \multicolumn{1}{|c|}{5} & & & \multicolumn{1}{|c|}{4} & & & \multicolumn{1}{|c|}{3} & & & \\ \cline{6-6} \cline{9-9} \cline{12-12}
& D & & & & & & & & & & & & 100 & \\
& & & & & & & & & & & & & & \\
\hline
& & & & & \multicolumn{1}{|c|}{8} & & & \multicolumn{1}{|c|}{4} & & & \multicolumn{1}{|c|}{3} & & & \\ \cline{6-6} \cline{9-9} \cline{12-12}
& E & & & & & & & & & & & & 300 & \\
& & & & & & & & & & & & & & \\
\hline
& & & & & \multicolumn{1}{|c|}{9} & & & \multicolumn{1}{|c|}{7} & & & \multicolumn{1}{|c|}{5} & & & \\ \cline{6-6} \cline{9-9} \cline{12-12}
& F & & & & & & & & & & & & 300 & \\
& & & & & & & & & & & & & & \\
\hline
\end{tabular}
\end{table}
\end{document}
This is the output: