Hey can someone please help me with this?

58. λ₀, is the threshold wavelength of a metal for photoelectron emission. If the metal is exposed to the light of wavelength λ, then the velocity of ejected electron will be $\sqrt{\frac{2\mathrm{h}}{\mathrm{m}}({\mathrm{\lambda }}_0-\mathrm{\lambda })\mathrm{K}}$. The value of K is:
​​​​​​​(A) speed of light
(B) 1
(C) $\frac{\mathrm{C}}{{\mathrm{\lambda }}_0\mathrm{\lambda }}$
(D) $\frac{1}{{\mathrm{\lambda \lambda }}_0}$