Current Attempt in Progress

What multiple of the time constant $\backslash (\backslash$tau $\backslash )$ gives the time taken by an initially uncharged capacitor in an $\backslash ($ R C $\backslash )$ series circuit to be charged to $\backslash (87\mathrm{.}6\backslash \%\backslash )$ of its final charge?

Number

Units