MWE:

```
\documentclass{scrbook}

\usepackage[showframe]{geometry}
\usepackage[draft]{graphicx}
\usepackage{blindtext}
\usepackage{subcaption}

\begin{document}

\begin{figure}
\begin{subfigure}{.5\textwidth}
    \centering
    \includegraphics[height=175px, width=200px]{dummy.png}
    \caption{left}
\end{subfigure}%
\begin{subfigure}{.5\textwidth}
    \centering
    \includegraphics[height=175px, width=150px]{dummy.png}
    \caption{right}
\end{subfigure}
\caption{\blindtext}
\end{figure}

\end{document}

```

and a picture:

![a busy cat](https://i.imgur.com/DsAZVWD.png)

How can I arrange the subfigures so that the space between the right fig and the right border equals the space between the left fig and the left border? I marked the space with red lines.

Any help is appreciated.