Answer
$L=0.313H$
Work Step by Step
$
\text { } L=\frac{\varepsilon_m}{\omega_d I_2}\left(1-2 \frac{\tan \phi_1}{\tan \phi_{\mathrm{o}}}\right)\\=\frac{120 \mathrm{~V}}{2 \pi(60.0 \mathrm{~Hz})(2.00 \mathrm{~A})}\left(1-2 \frac{\tan 10.0^{\circ}}{\tan \left(-20.0^{\circ}\right)}\right)\\=0.313 \mathrm{H} \text {}
$
