In how many years will a sum of money double itself at `6 1/4%` simple interest per annum?

In how many years will a sum of money double itself at 10 % per annum simple interest ?

In certain years a sum of money is doubled itself at 6(1)/(4)% simple interest per annum. then the required time will be

In how many years will a sum of money double itself at 18.75% per annum simple interest? (a) 4 years 5 months (b) 5 years 4 months (c) 6 years 2 months (d) 6 years 5 months

In what time will a sum of money double itself @ 20% per annum (p.a) simple interest ?

In what time will a sum double itself at 4% per annum, at simple interest ?