\documentclass[12pt]{standalone} 

\usepackage{pgfplots} 

\pgfplotsset{compat=1.18} 

\usetikzlibrary{patterns}

\usepgfplotslibrary{fillbetween}

\begin{document} 

\begin{tikzpicture}

    \begin{axis}[xmin=-1.1,xmax=5,ymin=-1.1,ymax=5,axis lines=center,

        xtick={3},

        ytick={4},

        xlabel=$x$, ylabel=$y$,

        ]

        \addplot[color=purple,thick,name path=upper] {(1-x/3)*4};

        \addplot[name path=lower] {5.2};

        \addplot[red,pattern=north west lines, pattern color=blue] fill between [of=upper and lower];

        \node[below left] at (0, 0) {$O$};

        \node[below left] at (1.5, 2) {$d$};

    \end{axis}

    \end{tikzpicture}

\end{document}