For a batch reactor, starting from $d\frac{x}{d}t=-ra\frac{V}{N}AO($mole balance$),$ assuming first order reaction and

$V=Vo,$

combine mole balance, rate law and stoichiometric relations, and

A$)$ Obtain an equation for time which is a function of $x.$

B$)$ For $K=0\mathrm{.}001s^{**}-1,$ using your result in part a$,$ calculate time necessary for given conversions.