very close:
\documentclass[tikz, border=1cm]{standalone}
\begin{document}
\begin{tikzpicture}
\draw[fill=black] (0,0) rectangle (12,6);
\draw[fill=white] (0,0) -- (12,6) -| cycle;
\draw[fill=white] (3,3) circle [radius=3cm];
\draw[fill=white] (9,3) circle [radius=3cm];
\draw (0, 0)--(12,6);
\end{tikzpicture}
\end{document}

more close:
\documentclass[tikz, border=1cm]{standalone}
\begin{document}
\begin{tikzpicture}
\draw[fill=black] (0,0) rectangle (12,6);
\fill[white] (0,0) -- (3,0) -- (3,3) -- cycle;
\draw[fill=white] (0,0) -- (12,6) -| cycle;
\draw[fill=white] (3,3) circle [radius=3cm];
\draw[fill=white] (9,3) circle [radius=3cm];
\draw (0, 0)--(12,6);
\end{tikzpicture}
\end{document}
