In Fig. $27.26$, take $\mathcal{E}_{0}=11 \mathrm{~V}, R=3.0 \Omega$, and $L=18 \mathrm{H}$. Initially the switch is in position $B$ and there's no current anywhere. At $t=0$ the switch is thrown to position $A$, and, at $t=15 \mathrm{~s}$, it's returned to $B$. Find the inductor current at (a) $t=7.50 \mathrm{~s}$ and (b) $t=22.5 \mathrm{~s}$.