Given that the inverse trigonometric functions take principal values only. Then, the number of real values of $x$ which satisfy $\sin ^ { - 1 } \left( \frac { 3x } { 5 } \right) + \sin ^ { - 1 } \left( \frac { 4x } { 5 } \right) = \sin ^ { - 1 } x$ is equal to:\\
(1) 2\\
(2) 1\\
(3) 3\\
(4) 0