A photon of wavelength λ is scattered from an electron, which was...

A photon of wavelength $\lambda$ is scattered from an electron, which was at rest. The wavelength shift $\Delta \lambda$ is three times of $\lambda$ and the angle of scattering $\theta$ is $60^{\circ}$. The angle at which the electron recoiled is $\phi$. The value of $\tan \phi$ is : (electron speed is much smaller than the speed of light)