Remove the 20 uF capacitor, since it is not part of the circuit we wish to simplify. Replace it with a short, since for a Norton, we need to find the short circuit current. Compute the current through the short (perhaps using mesh-current analysis). Then find the Norton Resistance. Since this is the same as the Thevenin Resistance, you must open the terminals where the capacitor was (rather than shorting them as we did in the first step).
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