Use the "Rule of $72"$ to determine the following:

$($a$)$ The number of years it takes to accumulate $$10,000$ in a savings account when $P=$$$5,000$ and $i=10\%$ per year.

$($b$)$ The number of years it takes to accumulate $$20,000$ in a savings account when $P=$$$5,000$ and $i=10\%$ per year.

$($c$)$ The average annual interest rate, $i,$ required to double an initial investment, $P,$ in $16$ years.

$($a$)$ The number of years it takes is $q,($Round to one decimal place.$)$

$($b$)$ The number of years it takes is $q,($Round to one decimal place.$)$

$($c$)$ The average annual interest rate is $\%($Round to two decimal places.$)$