The equation of the wavelength of the bremsstrahlung

In my text book, I came across this question:

What is the equation used to determine the shortest wavelenght of the bremsstrahlung spectrum of x-rays?

That represents all the kinetic energy gained by an electron $eV$ becoming a photon of energy $\frac {hc}{\lambda}$.
If the cut off wavelength for the continuous spectrum was $1\,\rm Å$ (corresponding to an electron energy of approximately $12 \,\rm kV$) then the K-lines would be produced from the Copper target but not from the Molybdenum target. So the shortest wavelength of the continuous spectrum must be less than the wavelength of a characteristic X-ray line.
In the case of Molybdenum the minimum energy of the incoming electron has be be approximately $18 \,\rm kV$ (photon wavelength $0.7\,\rm Å$) to produce a K-line.