\documentclass[10pt, a4paper]{article}

\usepackage{amsthm,amssymb,amsmath}

\usepackage[top=35mm, bottom=35mm, left=30mm, right=30mm]{geometry}

\usepackage{graphicx}

\usepackage{rotating}

\usepackage{multirow}

\usepackage{xepersian}
\settextfont[Scale=1]{XB Zar}


\setdigitfont[Scale=1]{XB Zar}

\begin{document}
\begin{sideways}
 \begin{tabular}{l l l l l }
       \hline
$x$ & $N = 5$ & $N = 8$ &$ N = 10$ & $N = 15$\\ 
       \hline
 \end{tabular}
\end{sideways}
\end{document}