please show work $($calculations $+$ formulas$)$

$2.$ We sometimes need to find how long it will take a sum of money $($or anything else$)$ to grow to some specified amount. Note that you should enter PV as a negative and FV as a positive.

$($a$)$ For example, if a company$$s sales are growing at a rate of $4\mathrm{.}80\%$ per year, approximately how long will it take sales to triple? Show your answer to $2$ decimals $($x$.$xx years$).$ If you are not sure how to work this, go back to this week$$s practice problems. Do not approximate using the $$rule of $72.$

If you are in doubt here, go back to the practice problems where double$/$tripling is discussed.

$($b$)$ If you want an investment to double in twelve years, what interest rate must it earn? Show your answer to $2$ decimals $($x$.$xx$\%).$