A certain sum becomes 3 times itself in 6 years at simple interest. In how many years will it become 9 times itself ?

A certain sum becomes 3 times itself in 4 years at compound interest. In how many years does it become 27 times itself ?

A sum of money triples itself in 3 years at compound interest. In how many years will it become 9 times itself ?

If certain sum becomes 3 times itself in 4 years at compound interest, in how many years will the sum become 81 times itself at the same rate of interest?

A certain sum of money triples itself in 6 years at compound interest. In how many years will it become 27 times at the same rate of compound interest?

A certain sum becomes 4 times in 7 years, at simple interest, then in how many years it will become 16 times?

A sum of money becomes 3 times of itself in 6 years at compound interest. In how many years will it become 81 times?