Respuesta :

There are 1000 milligrams, or mg, in one gram, or g.  Therefore, we have 400/1000=4/10=.4 grams in 400 milligrams.  The fourth answer is the best one.
[tex]m=0.001\ some\ unit\\\\400\ mg=400\cdot0.001\ g=\boxed{0.4\ g}[/tex]