The subject of this particular excercise is

a) to calculate the θ angle of the impendance given, which is Ż= 40^θ and

b) To calculate the frequency (f) in H.

It's an RL circuit, and the given values are L= 0.04 H and R = 20Ω.

The formulas that come to my mind are the Ż = √(R² + X²L) and L= XL/2πf, but I obviously can't use them and I'm stuck. I'd appreciate any help!