Tritium is radioactive with a half$-$life of $12\mathrm{.}33$ years decaying into $3He.$ If we have a sample of $3E18$ tritium atoms, what is its activity in decays$/$second$?(1$year $=3\mathrm{.}15E7s)$

$5\mathrm{.}35$E$9/$second

$3\mathrm{.}69$E$8/$ second

$6\mathrm{.}64$E$7/$second

$4\mathrm{.}20$ E$10/$second