A person said : Take my age three years hence, multiply it by 3 and then subtract 3 times my age three years ago and hence everybody will know how old I am ". The age of person in years is:

Let us assume the present age of the person be P years.
3 years hence the age of person = P + 3
3 years ago the age of person = P - 3
According to question,
Take my age three years hence, multiply it by 3 and then subtract 3 times my age three years ago,
= 3(P + 3) - 3(P - 3)
= 3P + 9 - 3P + 9
= 18 years
Hence, age of the person = 18 years