A chemist has 80 pints of a 20% iodine solution. How many pints of iodine must be added to produce a solution that is 33.1/3% iodine?

Question

Please help me work this through

Let X be the number of pints of iodine that must be added.
You start out with a mix that contains 16 pints of pure iodine and 64 of solvent. You keep the amount of solvent the same and add X pints of iodine. The new fraction of iodine is
(16 + X)/(80 + X) = 1/3
16 + X = 80/3 + X/3
(2X/3) = 32/3
X = ?