Your Grandfather upon your birth invested $$5000$ into an account for you. The account has earned an annual rate of $16\%$ a year. On your $21$st birthday you could withdraw the accumulated amount. How much can you withdraw?

Now suppose, there is $$50804$ in the account. What rate of return did we receive?

I want to have $$60000$ on my $21$st birthday. If I could have earned $13\mathrm{.}2\%$ a year, how much would my grandfather have had to invest in the account for me to reach $$60000?$