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

In what time will a sum of money double itself at 15% per annum?

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

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

In what time will a sum become three times itself at 20% per annum, at simple interest?

In what time will Rs. 3600 amount to Rs. 4320 at 4% per annum simple interest?

What is the principal? I. The simple interest accrued on that sum at the rare of 12% per annum in 2 years is Rs. 360 less than the compoind interest on the same sum at 12% per annum in 2 years. II. The sum doubles itself in 10 years at 10% per annum rate of simple interest. III. The compoind interest on teh sum in 2 years at the rate of 12% per annum is Rs.6360.

In how many years will a certain sum amounts to 6 times itself at 25% per annum simple interest ?