if A= 3x and B= x
your equation will look like: 3x + x = 200
combine like terms to get 4x = 200
then, divide each side by 4 to get x = 50
if x = 50, then patient B receives 50 mg. to find A, you can either subtract 50 from 200 or you can take 50 multiplied by 3. patient A receives 150 mg.
