השלמת לוח חיבור

‎\begin{array}{c|c}
\hline
+ & 2 & 6 & 1 \\
\hline
9 & \INPUTBOX{4}{ltr}{11} & \INPUTBOX{5}{ltr}{15} & \INPUTBOX{6}{ltr}{10} \\
\hline
\INPUTBOX{1}{ltr}{2} & \INPUTBOX{2}{ltr}{4} & 8 & \INPUTBOX{3}{ltr}{3} \\
\hline
\INPUTBOX{7}{ltr}{10} & 12 & \INPUTBOX{8}{ltr}{16} & \INPUTBOX{9}{ltr}{11} \\
\end{array}