Let the first amount be x and the second y.

We have: x + y = 2000 and

x − y = 660

Adding gives 2x = 2660 so x = 1330, then y = 670.

Checking: x + y = 1330 + 670 = 2000 (OK)

x − y = 1330 − 670 = 660 (OK)

So the amounts of dosage should be 1330 mg for the first patient and 670 mg for the next patient.