We need to use consistent units throughout. The 2 g of drug is equivalent ot 2000 mg.

Rough estimate: We expect the dosages to be around 700 mg and 1300 mg, based on similar thinking to Example 1 above.

Let the amount the adult gets be d mg.

The child will get d − 660.

Together, the two dosages must be: d + (d − 660) = 2000

That is 2d − 660 = 2000

2d = 2660

d = 1330

And d − 660 = 1330 − 660 = 670

So the adult gets 1330 mg and the child gets 670 mg.