Question Difficulty

A $0\mathrm{.}320*$kg croquet ball makes an elastic head$-$on collision with a second ball initially at rest. The second ball moves off with half the original speed of the first ball.

$($a$)$ What is the mass of the second ball?

$\backslash$times $,$kg$()/(\_(()/())$K$)($E$)/($K$)$E gets transferred to the second ball?

$\%$