The Ka X-ray emission line of tungsten occurs at I = 0.021 nm. The energy difference between K and L levels in this atoms is about:
(IIIT JEE 1997)
We know that, the energy difference is carried by the photon. So, the energy of the mentioned photon will give us the desired result.
E=hcλ=1240eV0.021=59,047eV
Which is approximately equal to 59KeV