Determine the inductive time constant if the current in an RL circuit builds up to one$-$third of its steady$-$state value in $5\mathrm{.}00$s$.$

A$\mathrm{.}12\mathrm{.}3$s

B$\mathrm{.}7\mathrm{.}5$s

C$.9$s

D$.2\mathrm{.}5$s