Current Attempt in Progress

Outside the nucleus, the neutron itself is radioactive and decays into a proton, an electron, and an antineutrino. The half$-$life of a neutron $($mass $=1\mathrm{.}675{10}^{-27}kg)$ outside the nucleus is $10\mathrm{.}4$ min $.$ On average, over what distance $x$ would a beam of $5\mathrm{.}10-eV$ neutrons travel before the number of neutrons decreased to $75\mathrm{.}0\%$ of its initial value? Ignore relativistic effects.

$x=$