You have $$20,000$ to invest for $10$ years.

a$.$ How much additional interest will you earn if the investment provides a $10\%$ annual return, compared to a $8\%$ annual return?

b$.$ How long will it take your $$20,000$ to double in value if it earns $10\%$ annually?

c$.$ What annual rate has been earned if $$5,000$ grows into $$8,000$ in $10$ years?