what is the interest rate on an account that took 15 years to double if interest was compounded continuously and no deposits or withdrawals were made during the 15 year period?

If you deposit 5000RS into an account paying 8.25% annual interest compoundedsemiannually, how long until there is 9350RS in the account

In its first 10 years a mutual fund produced an average annual return of 19.72%. Assume that money invested in this fund continues to earn 19.72% compounded annually. How long will it take money invested in this fund to double? It will take approximately (Round up to the nearest year.) year(s) for the money invested in this fund to double.

Now imagine you are 25 years old. Use the same value of P from 1), above, but do this: Deposit P dollars a month into an account that pays 7% compounded monthly. Do this until you are 35 years old.  Then, at age 35, you stop putting money into the account.  You will make no more deposits into the account, but the money that you already have in it will continue to earn 7%, compounded monthly, until you reach age 65.  Find the amount in your account at age 65. How much of your own money did you deposit? How much total interest did you earn? P=$400