The figure given below shows an LCR series circuit with two switches $S_1$ and $S_2$. When switch $S_1$ is closed keeping $\mathrm{S}_2$ 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 $\left(3 L_1-L_2\right)$ is $\_\_\_\_$ H. $$ \left(X_{L 1}>X_C, X_{L 2}>X_C\right) $$