Answer
$t=17\ h$
Work Step by Step
For a first-order reaction;
$ln(C/C_0)=-k.t; k=0.693/t_{1/2}$
$ln(2.00\times10^{-4}\ mol/L\div 3.6\times10^{-3}\ mol/L)=-0.693/245\ min\times t$
$t=1021.85\ min=17\ h$
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