How to find the frequency of the AC source in RL circuit?
Finally I found the answer:

$$R_f=R_L+R=33\Omega$$
$$\phi=arcos(0.819)=35.01$$
$$tg\phi=\frac{X_L}{R_f}\Rightarrow X_L=tg\phi* R_f=23.11$$
$$X_L=\omega L=2\pi fL \Rightarrow f=\frac{X_L}{2*\pi}\frac{1}{L}=\frac{23.11}{2\pi 0.04}= 91.95 Hz$$
Correct answer is e) 92Hz