[tex]\begin{gathered} \frac{5.7365\cdot10^{-5}}{3.4891\cdot10^{-8}}= \\ =\frac{5.7365}{3.4891}\cdot\frac{10^{-5}}{10^{-8}}=\text{ separating by similar terms} \\ =1.64412026\cdot10^{-5-(-8)}=\text{ calculating each division separately} \\ =1.6441\cdot10^3\text{ rounding} \end{gathered}[/tex]
Both numerator and denominator have 5 significant figures, then the quotient will have 5 significant figures too.