\documentclass{standalone}
\usepackage{tikz}
\usepackage{siltex}
\usetikzlibrary {arrows.meta,positioning}
\tikzset{nodes={text height=.7em, text width=2.8cm, align=center,
draw=black!50, thick, font=\footnotesize, fill=white},
>={Stealth[round,sep]}, rounded corners, semithick}

\begin{document}
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    \draw[fill=lightgray] (-1.7cm,-3cm) rectangle (5cm, -7.2cm);
    \node (pd) {Problem Description};
    \node (sp)[below=1 of pd]  {System\\Requirements};
    \node (id)[below=1 of sp]  {Initial Design};
    \node (fs)[below=1 of id]  {Feature Definition};
    \node (ss)[below=1 of fs]  {Feature Selection};
    \node (a1)[below=0.8 of ss,draw=none, fill=none] {};
    \node (rd)[below=0.8 of a1]  {Rapid Development};
    \node (va)[right=1 of a1]  {Variable Approach};
    \path[->] (pd) edge (sp)
              (sp) edge (id)
              (id) edge (fs)
              (fs) edge (ss)
              (ss) edge (rd)
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              (va) edge[bend right] (ss.east);
    \draw (3.4cm,0cm) node[draw=none, fill=none,text width=2.9cm] (wf) {Systems Engineering:\\Waterfall};
    \node (ridm)[right=1 of fs, fill=none, draw=none] {Rapid Iterative Design Method};
\end{tikzpicture}
\end{document}