The voltage applied across an X-ray tube is doubled. What happens to the cutoff wavelength in the

Question:

The voltage applied across an X-ray tube is doubled. What happens to the cutoff wavelength in the spectrum of wavelengths emitted by the tube's metal target?
(a) It also doubles.
(b) It decreases by a factor of two.
(c) It increases by a factor of four.
(d) It decreases by a factor of four.
(e) Nothing happens to it.