A deposit of $$500$ made five years ago is worth $$705\mathrm{.}30$ today. The deposit pays interest semi$-$annually. What is the interest rate?  

How much would you have had to invest $21$ years ago in an account paying $6\%$ compounded annually to cover the cost of a $$15,000$ engagement ring for your fiance?

Approximately how many years must one wait for an initial investment of $$10,000$ to triple in value if the investment earns $9\%$ compounded annually?

During one year on a $$250$ deposit paying continuously compounded interest at an APR of $8\%,$ how much interest can be accumulated?