Oxide layer formation on a metal is a $Rx_n$ which is of first order with rate constant $10^{-8}min^{-1}$ if maximum thickness can be $2mm$ then what time will be taken to form a oxide layer of thickness $1.5mm$

Question

$\begin{array}{1 1} 1.386 \times 10^{8}\;min \\ 0.693 \times 10^{8}\;min \\ 10^{8}\;min \\ 4.238 \times 10^{8}\;min\end{array}$