Frequency in RL Circuit
\$I=\sqrt{\dfrac{P}{R}}\$   = Apparent current.  

What is ω?  \$I=\dfrac{V}{Z}=\dfrac{V}{\sqrt{R^2+{ωL}^2}}\$

so \$\sqrt{\dfrac{P}{R}}=\dfrac{V}{\sqrt{R^2+{ωL}^2}}\$ 
and

\$\dfrac{P}{R}=\dfrac{V^2}{R^2+ωL^2}\$ and   

solve for ω