The figure given below shows an LCR series circuit with two switches \( S_1 \) and \( S_2 \). When switch \( S_1 \) is closed keeping \( S_2 \) open, the phase difference \( (\phi) \) between the current and source voltage is \( 30^\circ \) and phase difference is \( 60^\circ \) when \( S_2 \) is closed keeping \( S_1 \) open. The value of \( \left(3L_1 - L_2\right) \) is ________ \( \text{H} \\).
