Welcome aboard!
On the long run, you would benefit by learning the pen tool and how to trace images manually.
Can hardly suggest one specific tutorial, though it is the very basic of vector graphics.
Maybe have a look at
these, or browse though
these.
BUT if it's for a "quick fix", there is always a cheapo solution.
Inkscape uses potrace, which doesn't produces "single lines" as autotrace.
Thus, you need to fill in the areas in your raster images -in a raster editor, like gimp.
The bucket fill tool can get you there straight with the first image, the other one would need a bit of painting here and there.