For the first order reaction ${\mathrm{t}}_{99.99\mathrm{\%}}=\mathrm{x}.{\mathrm{t}}_{90\mathrm{\%}}$. Find the value of x

For first order reaction $\mathrm{kt}=\ln \frac{\left[\mathrm{Ao}\right]}{\left[\mathrm{At}\right]}\mathrm{A}\to \mathrm{Pt}=0$
Ao $\mathrm{t}={\mathrm{t}}_{0.9999}0.0001{\mathrm{A}}_0\mathrm{t}={\mathrm{t}}_{0.90}0.1{\mathrm{A}}_0\frac{{\mathrm{t}}_{0.9999}}{{\mathrm{t}}_{0.90}}=\frac{\ln {\displaystyle }{10}^4}{\ln {\displaystyle }10}=4$