A certain quantity of money becomes three times in `20` years , then at the same rate of interest in how many years it will become double?

A certain sum of money becomes three times of itself in 20 yr at simple interest. In how many years, does it become double of itself at the same rate of simple interest ?

A certain sum of money becomes three xx of itself in 20 years at simple interest.In how many years does it become double of itself at the same rate of simple interest?

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