Find the Expression as the Tangent of an Angle $\frac { \tan 3 x + \tan x } { 1 - \tan 3 x \tan x }$

Multiple Choice

Find the expression as the tangent of an angle. $\frac { \tan 3 x + \tan x } { 1 - \tan 3 x \tan x }$

A) $\tan 2 x$
B) $\tan 3 x$
C) $\tan 4 x$
D) $\tan ^ { - 1 } 4 x$
E) $\tan ^ { - 1 } 2 x$