The effective impedance of the two branches in parallel is 2.3k \/ -8 deg or 2.3k - j0.3k
Answer for 4.38
The current through the voltage source is 2.1 A \/ -45 deg.
Answer for 4.39
The voltage across the current source is 11 V \/ -56 deg.
Answer for 4.44
The effective impedance of the network is purely resistive at the specified frequency: 1 ohm.