For adults, the RDA of the amino acid lysine is 12 mg per kg of body weight. How many grams per day should a 71.0kg adult receive?

Convert the given density in mg/kg to g/kg by the dimensional analysis. This is shown below,

(12 mg/kg) x (1 g / 1000 mg) = 0.012 g/kg

Multiply this quantity with the weight of the adult given above,

(0.012 g/kg) x (71 kg) = 0.852 g

Thus, the adult should receive 0.852 g of lysine.