\documentclass[12pt, varwidth, border=5mm]{standalone}
\usepackage{tikz}
\usepackage{amsmath}
% Underlining package
\usepackage{ulem}
\usetikzlibrary{calc}
\usetikzlibrary{angles,quotes}
% \usepackage[a4paper, portrait, margin=1cm]{geometry}

\begin{document}
\section*{ }
    \begin{minipage}{0.55\textwidth}
  \begin{tikzpicture}[scale=1.0, baseline=(current bounding box.north)]
    \begin{scope}[rotate=0]

        \coordinate (E) at (0,0);
        \coordinate (F) at (4.316,0);
        \coordinate (H) at (3.761,0);
        \coordinate (G) at ($(H)+(0,1.918)$); % Perpendicular upwards

        \draw (E)--(F)--(G)--cycle;
        \draw[dashed] (H)--(G);
        \pic [draw, -, angle radius=0.2cm] {right angle=G--H--F};

        % Vertex LABELS
        % Labels relative to shape geometry
        \node at ($(E)+(-0.2,-0.2)$) {E};
        \node at ($(F)+(0.2,-0.2)$) {F};
        \node at ($(H)+(0.0,-0.2)$) {H};
        \node at ($(G)+(0.2,0.2)$) {G};


        % dotted/dashed arrows shifted away from edges
        % Horizontal side (A-B), shifted down yshift=0mm,
        \draw[<->, gray]
            ($(E) + (0,-0.7cm)$) -- ($(F) + (0,-0.7cm)$)
            node[black, midway, fill=white, inner sep=2.5pt] {9\,cm};

        % Vertical side (B-C), shifted right xshift=0mm,
        \draw[<->, gray]
            ($(F |- H)+(0.6,0)$) -- ($(F |- G)+(0.6,0)$)
            node[black, midway, fill=white, inner sep=2.5pt] {4\,cm};

    \end{scope}
\end{tikzpicture}
\end{minipage}%
\hfill
\begin{minipage}{.4\textwidth}
  \begin{align*}
    \text{Area} &= \frac{1}{2} \text{bh} \\
    \text{Area} &= \frac{1}{2} \times 9 \text{cm} \times 4 \text{cm}  \\
    \text{Area} &= 18.0 \text{cm}^2
  \end{align*}
\end{minipage}

\end{document}