I am trying to to get the smaller images in the second row to center align with the bigger images in the first row: (this using MS word)

I tried the following code:
\begin{figure*}[h]
\centering
\subcaptionbox{} [4em] {\includegraphics[width=8em]{4a.png}}\hfill
\subcaptionbox{} [4em] {\includegraphics[width=8em]{4b.png}}\hfill
\subcaptionbox{} [4em] {\includegraphics[width=8em]{4c.png}}\hfill
\subcaptionbox{} [4em] {\includegraphics[width=8em]{4d.png}}\hfill
\subcaptionbox{} [4em] {\includegraphics[width=8em]{4e.png}}\hfill
\subcaptionbox{} [4em] {\includegraphics[width=8em]{4f.png}}\\
\subcaptionbox{} [4em] {\includegraphics[width=4em]{4g.png}}\hfill
\subcaptionbox{} [4em] {\includegraphics[width=4em]{4h.png}}\hfill
\subcaptionbox{} [4em] {\includegraphics[width=4em]{4i.png}}\hfill
\subcaptionbox{} [4em] {\includegraphics[width=4em]{4j.png}}\hfill
\subcaptionbox{} [4em] {\includegraphics[width=4em]{4k.png}}\hfill
\subcaptionbox{} [4em] {\includegraphics[width=4em]{4l.png}}
\caption {My caption}
\end{figure*}
But, as you see, I have to manually adjust the hspace values to make each of the smaller images center aligned with their corresponding bigger images. How should I go about it?


\subfigures? – Werner Nov 02 '18 at 19:54subcaption. – Werner Nov 02 '18 at 19:56