For adults, the rda of the amino acid lysine is 12 mg per kg of body weight. how many grams per day should a 70 kg adult receive?

The important part of this problem is the conversion part and the calculation part.
We already know that
1 mg = 0.001 gm
Then
For 1 kg adult, the amount of amino acid lysine required is = 12 mg
                                                                                               = (12 * 0.001) gm
                                                                                               = 0.012 gm
So
For a 70 kg adult the amount of amino acid lysine required is = 0.012 * 70 gram
                                                                                                   = 0.84 grams
so for an adult weighing 70 kg, the amount of amino acid lysine required is 0.84 grams. I hope the procedure is clear enough for your understanding. Based on this procedure , you can always solve similar problems without requiring any outside help.