I know the formula for this is FVn = PV(1+r)^n, but I am not sure how to solve for n through that.

I have tried using financial calculators online, but there is an error because it says I need a PMT, even though that is not provided. I put in 0 and it still has an error. If someone could solve this, and either write out how to solve for n, or provide a link to a financial calculator that works, I'd appreciate it. Thank you.

(Compound value solving for n) How many years will the following take? a. $520 to grow to $1,476.50 if invested at 11 percent compounded annually b. $35 to grow to $69.74 if invested at 9 percent compounded annually c. $105 to grow to $455.12 if invested at 13 percent compounded annually d. $53 to grow to $70.93 if invested at 6 percent compounded annually