Answer
$\phi_i=73.9^{\circ} \text {. }
$
Work Step by Step
$
\text { } \phi_i=\tan ^{-1}\left(2 \tan 60.0^{\circ}\right)\\=73.9^{\circ} \text {. }
$
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.