A first order reaction has a rate constant of $15 \times 10^{-3}S^{-1}$. How long will $5.0 \;g$ of this reactant take to reduce to $3.0 \;g$?

Question

$\begin{array}{1 1} 35\;sec \\ 34.07\;sec \\38\;sec \\39\;sec \end{array}$