From the plot, $\mathrm{t}_{1 / 2} \propto[\mathrm{~A}]_0$ $$ \begin{align*} & \propto\left[\mathrm{A}_0\right]^{1-\mathrm{n}} \\ & 1-\mathrm{n}=1 \\ & \mathrm{n}=0 \text { (order) } \\ & \mathrm{t}_{1 / 2}=\frac{\mathrm{A}_0}{2 \mathrm{~K}} \\ & 240=\frac{4 \times 10^{-3}}{2 \mathrm{~K}} \tag{1}\\ & \mathrm{x}=\frac{1.5 \times 10^{-3}}{2 \mathrm{~K}} \tag{2} \end{align*} $$ Divide (1) / (2) $$ \begin{aligned} & \frac{240}{x}=\frac{4}{1.5} \\ & x=90 \end{aligned} $$