Question $2$: LR Circuit $(30$ Points$)$

The circuit shown is composed of a $L=3H$ inductor, three $R=1\mathrm{.}5$ resistors, and a $=12V$ voltage supply.

a$.(5$ points$)$ What is the current while switch $2$ has been opened and switch $1$ has been closed for a long amount of time?

b$.(10$ points$)$ After switch $1$ is closed and switch $2$ is opened, how long does it take for the current to reach $2$ A $?$

c$.(10$ points$)$ After switch $1$ has been closed for a long time, switch $1$ is opened again and switch $2$ is closed. How long does it take for the current to reach $3$ A $?$