Please be a little more specific on what you want to ask.
I can be of some help.
The ratio is 2:3 for the side lengths of the triangles.
so 6:9 is one side and 5:x would be the other side
2/3 of five is 3.33 and multiplying that by 2 gives you 6.67
Polygons are similar? Well there is no picture provided, so I have no idea what you're talking about. But I think you might be asking if in general all polygons are similar, and if that's the case, they are not. Similar means they are similar in at least one aspect, and all polygons are different from each other, only adding one line for each bigger polygon. So I don't know if this helped you, but I tried anyways.
