A $12\mathrm{.}0$ V battery is connected into a series circuit containing a $12\mathrm{.}0$ resistor and a $2\mathrm{.}30$ H inductor.

$($a$)$

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

s

$($b$)$

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