A $12\mathrm{.}0$ V battery is connected into a series circuit containing a $\backslash (16\mathrm{.}0\backslash$Omega $\backslash )$ resistor and a $2\mathrm{.}90$ H inductor.

$($a$)$ In what time interval $($in s$)$ will the current reach $\backslash (50\mathrm{.}0\backslash \%\backslash )$ of its final value?

s

$($b$)$ In what time interval $($in s$)$ will the current reach $\backslash (90\mathrm{.}0\backslash \%\backslash )$ of its final value?

s

What If$?$ After a very long time, using a switch like that shown in the figure below, the battery is removed and the inductor is connected directly across the resistor.

$($c$)$ In what time interval $($in s$)$ will the current decrease to $\backslash (50\mathrm{.}0\backslash \%\backslash )$ of its initial value?

s

$($d$)$ In what time interval $($in s$)$ will the current decrease to $\backslash (10\mathrm{.}0\backslash \%\backslash )$ of its initial value?