Welcome kanyi!
You just need to draw 1 line, set it at the angle you need, and then Duplicate to get the other line, and move it wherever you need it.
There are probably a few ways to set the line at a specific angle -- 2 that I can think of at the moment. Generally you can use Object menu > Transform > Rotate. Specifically, I would need to know what is the reference for that angle, to tell you exactly how to do it. (Also need to know how your preferences are set, see below.)
Different fields of endeavor use different standards for that. So is it 54.7? from a horizontal line, or vertical line? Or could it be 54.7? relative to another line? Or could that be navigational, like if you are hiking and using a compass to find your way (sorry, I can't remember the proper terminology for that). You may need to do some simple math, depending on which kind of measurement you need.
In Inkscape, you can set whether you want mathematical type angles or compass-like, in Inkscape Preferences > Behavior > Steps > Use compass-like display of angles. Info from the manual is at the bottom of this page:
http://tavmjong.free.fr/INKSCAPE/MANUAL/html/Coordinates.htmlLet us know if that answers your question. As I mentioned, there are other ways to do it, if the Transform dialog doesn't work for this case.
