The charge in a capacitor is given by:
[tex]Q=CV[/tex]Plugging the values of the charge anf the potential differnce and solving for the capacitance we have:
[tex]\begin{gathered} 8.6\times10^{-6}=3.5C \\ C=\frac{8.6\times10^{-6}}{3.5} \\ C=2.5\times10^{-6} \end{gathered}[/tex]Therefore the capacitance is:
[tex]2.5\times10^{-6}\text{ F}[/tex]