\documentclass[]{article}
\usepackage[utf8]{inputenc}
\usepackage{fourier}
\usepackage{SIunitx}
\usepackage{amsmath,amssymb,amsfonts}
\usepackage{tikz}
\usetikzlibrary{calc,3d}

\begin{document}
\begin{minipage}{0.4\textwidth}
\begin{tikzpicture}[x  = {(-0.5cm,-0.5cm)},
                    y  = {(0.9659cm,-0.25882cm)},
                    z  = {(0cm,1cm)},
                    scale = 4,
                    color = {lightgray}]
% style of faces
\tikzset{facestyle/.style={fill=lightgray,draw=red,very thin,line join=round}}
% face "back"
\begin{scope}[canvas is zy plane at x=0]
  \path[facestyle,shade] (0,0) rectangle (1.8,0.6);
\end{scope}
% face  "left"
\begin{scope}[canvas is zx plane at y=0]
  \path[facestyle,shade] (0,0) rectangle (1.8,1.45);
\end{scope}
% face "front"
\begin{scope}[canvas is zy plane at x=1.45]
  \path[facestyle] (0,0) rectangle (1.8,0.6);
\end{scope}
% face  "right"
\begin{scope}[canvas is zx plane at y=0.6]
  \path[facestyle] (0,0) rectangle (1.8,1.45);
\end{scope}

%face "up"
\begin{scope}[canvas is yx plane at z=1.8]
  \path[facestyle] (0,0) rectangle (0.6,1.45);
\end{scope}

% labels
\draw[very thin,black,line join=round]
     (0,0.6,1.8) -- node [below] {$a$}
     (1.45,0,1.8) -- node [right]        {$b$}
     (1.45,0.6,0) -- node [left] {$c$}
     (0,0.6,1.8);
\draw[very thin, gray,dashed,line join=round]
    (0,0,0)--
    (1.45,0,0) -- node[left]{$d$}
    (0,0.6,1.8);
\draw[very thin, gray,dashed,line join=round]
    (0,0.6,0)-- (0,0,0) -- (0,0,1.8);
\draw[very thin,black,|<->|]
    (0,-0.015,1.81) -- node[sloped,above,fill=white]{\SI{1,45}{\metre}}
    (1.45,-0.015,1.81);
    \draw[very thin,black,|<->|]
    (0,0.005,1.82) -- node[sloped,above,fill=white]{\SI{0,6}{\metre}}
    (0,0.605,1.82);
\draw[very thin,black,|<->|]
    (0,0.62,0.005) -- node[right]{\SI{1,8}{\metre}}
    (0,0.62,1.805);
\end{tikzpicture}
\end{minipage}
\hspace{0.2\textwidth}
\begin{minipage}[c]{0.4\textwidth}
\begin{align*}
    a&=\sqrt{(\SI{0,6}{\metre})^2+(\SI{1,45}{\metre})^2}\approx \SI{1,569}{\metre}\\
    b&=\sqrt{(\SI{0,6}{\metre})^2+(\SI{1,8}{\metre})^2}\approx \SI{1,897}{\metre}\\
    c&=\sqrt{(\SI{1,45}{\metre})^2+(\SI{1,8}{\metre})^2}\approx \SI{2,311}{\metre}\\
    d&=\sqrt{(\SI{0,6}{\metre})^2+(\SI{1,45}{\metre})^2+(\SI{1,8}{\metre})^2}\approx \SI{2,38799}{\metre}
\end{align*}
\end{minipage}
\end{document}