The wavelength of an electron and a neutron will become equal when...

${\lambda}_{e} = {\lambda}_{n}$

$\dfrac{h}{{m}_{e} . {v}_{e}} = \dfrac{h}{{m}_{n} . {v}_{n}}$

${\lambda}_{e} =$Wavelength of electron

${\lambda}_{n} =$Wave length of neutron

${m}_{e}and{M}_{n} =$Mass of electron and neutron respectively

${v}_{e}and{v}_{n} =$Velocity of electron and neutron respectively

$h = 6 . 626 \times {10}^{- 34}Js =$Planck's constant

${m}_{e} . x . {v}_{n} = {m}_{n} . {v}_{n}$

$x = \dfrac{{m}_{n}}{{m}_{e}} = \dfrac{1 . 6 \times {10}^{- 27}}{9 . 1 \times {10}^{- 31}}$

$⇒ x = \dfrac{16}{9} \times {10}^{3}$

$= 1 . 758 \times {10}^{3}$

$= 1758$