facing a difficult situation,Arnold decided to ask his boss

分词:-ing,-ed.
facing表示与Arnold的主动关系.是"Arnold面对a difficult situation"
faced with与compared with是一个用法:
如:compared with something 表示"与...相比".
所以"faced with a difficult situation,Arnold decided to ask his boss for advice" 应该是"与其去面对这种困难的局面(与去面对这种困难的局面相比),Arnold决定去向上司询问意见."