In other words, in 18 years, Luis will be 12 years older than Milla and she will be 2/3 of his age. It means that the difference 12 years of their ages at that time will be 1/3 of the Luis' age. Hence, in 18 years, Luis will be 36 years old, while Milla will be 36-12 = 24 years old. So now, Luis is 36-18 = 18 years old. ANSWER.