In the given circuit, the current $I_x$ (in mA) is _______ .

In the circuit given below, the switch $S$ was kept open for a sufficiently long time and is closed at time $t = 0$. The time constant (in seconds) of the circuit for $t > 0$ is _______ .

For the two port network shown below, the value of the $Y_{21}$ parameter (in Siemens) is ______.

In the network shown below, maximum power is to be transferred to the load $R_L$.

The value of $R_L$ (in Ω) is ______.