Complex Thevenin

The top circuit is an AC-excited RLC network with output terminals shown on the right. This can be represented as a Thevenin $RL$ -equivalent as seen from the output terminals.

Determine $R_{TH} + X_{TH}$

Note: The quantity $j$ is the imaginary unit. The letter $X$ denotes the reactance associated with the inductance

Note: In the second circuit, instead of $V_S$ , the source voltage should be $V_{TH}$ (copy paste error on my part)