A graph between $\log {\mathrm{t}}_{1/2}$ vs $\log \mathrm{a}$, with $\mathrm{a}$ being the initial concentration of $\mathrm{A}$ in the reaction $\mathrm{A}\to$ Product, is shown in the figure. 

Then the rate law is

Assuming gas-phase decomposition of dimethyl ether follows $1^{\mathrm{st}}$ order kinetics:

${\mathrm{CH}}_3-\mathrm{O}-{\mathrm{CH}}_3 \left(g\right)\to {\mathrm{CH}}_4 \left(g\right)+{\mathrm{H}}_2 \left(g\right)+\mathrm{CO} \left(g\right)$ 

The reaction is carried out in a constant volume container at $500°\mathrm{C}$ and has a half-life $14.5 \min$. Initially, only dimethyl ether is present at a pressure of $0.4 \mathrm{atm}$. The total pressure of the system after $12 \min$ is: (given $\log \left(1.8\right) = 0.249$)