the formula is distribution coefficient is equal to the concentration of solvent 1 divided by solvent 2.
Concentration *in* solvent 1, divided by concentration in solvent 2, right.
So initially you have 3 mmols of product in the CCl4
After one extraction you have 3-x mmols in the CCl4
, and x mmols in the aqueous, such that the ratio of their concentrations is equal to your distribution coefficient, so how much after one extraction?