An electron$-$positron pair is produced by a $2\mathrm{.}90$MeV$2\mathrm{.}90\backslash ,\backslash$text$\{$MeV$\}2\mathrm{.}90$MeV photon. What is the kinetic energy of the positron if the kinetic energy of the electron is $0\mathrm{.}469$MeV$0\mathrm{.}469\backslash ,\backslash$text$\{$MeV$\}0\mathrm{.}469$MeV?

Use the following conversion: $1$eV$=1\mathrm{.}6021019$J$1\backslash ,\backslash$text$\{$eV$\}=1\mathrm{.}602\backslash$times $10^\{-19\}\backslash ,\backslash$text$\{$J$\}1$eV$=1\mathrm{.}6021019$J$.$

The rest mass of an electron is $9\mathrm{.}111031$kg$9\mathrm{.}11\backslash$times $10^\{-31\}\backslash ,\backslash$text$\{$kg$\}9\mathrm{.}111031$kg$.$