Answer :

[tex]1g=1000mg\to1mg=0.001g\\\\1kg=1000g\\\\6.204mg=6.204\cdot0.001g=0.006204g\\\\0.00036kg=0.00039\cdot1000g=0.39g\\\\\\283.85g+6.204mg+0.00039kg=283.85g+0.006204g+0.39g\\\\=284.2462g[/tex]