The wavelength of electrons accelerated from rest through a potential difference of 40 kV is x $\times$ 10^$-$12 m. The value of x is ___________. (Nearest integer)

Give : Mass of electron = 9.1 $\times$ 10^$-$31 kg

Charge on an electron = 1.6 $\times$ 10^$-$19 C

Planck's constant = 6.63 $\times$ 10^$-$34 Js