The two steady states can be found by finding the equivalent current at
the switches.
When the switch is open, the 2 kΩ resistor is taken into account,
forming a Rt = 4 kΩ resistor with the lower one.
Thus by using an equivalent source, the voltage source becomes a
current one,
with a current of I = U/Rt = 8/4 = 2 mA
When the switch is closed, the 2 kΩ resistor is not taken into
account, thus Rt = 2 kΩ (only the lower one).
Thus by using an equivalent source, the voltage source becomes a
current one,
with a current of I = U/Rt = 8/2 = 4 mA
So when t < 0 we have iL(t) = 2 mA and when t > 0 then iL(t) = 4
mA