# Impedance of a circuit that contains a 2 port network

simulate this circuit – Schematic created using CircuitLab

So, firstly, find the y parameters of a network ( says the assignment). Which I did. Now for the impedance I get the a parameters (for the box), from those y.

I get $$\frac{V1}{I1}=\frac{ a_{11}*V_2 -a_{12}*I_2}{a_{21}*V_2-a_{22}*I_2}$$

Can I use this expression to find impedance of a whole circuit? That is, to express I2 as I2=Ig-V2/4 and plug that into above equation. Will that give me the correct result?