The Switch in the Circuit Shown Below Has Been Closed $t = 0$

Essay

The switch in the circuit shown below has been closed for a long time before it is opened at $t = 0$ . Find the current $i ( t )$ through the inductor for $t \geq 0$ . Assume $R _ { 1 } = 400 \Omega , R _ { 2 } = 2 k \Omega , R _ { 3 } = 1$ $\mathrm { k } \Omega , \mathrm { R } _ { 4 } = 6 \mathrm { k } \Omega , \mathrm { V } _ { \mathrm { s } } = 2 \mathrm {~V} , \mathrm {~L} = 90 \mathrm { mH }$ .