This very attractive geometrical puzzle is from Catriona Agg. It looks like there isn't enough information, although there is. See the Comments for my solution.
![](https://learn1.open.ac.uk/mod/oublog/pluginfile.php/15/mod_oublog/message/236344/purple-sun-question.jpg)
But even after solving it it still feels as though there is an information deficit somewhere!