(II) In Fig. $19-56$ (same as Fig. $19-20 a )$ , the total resistance is 15.0 $\mathrm{k} \Omega$ , and the battery's emf is 24.0 $\mathrm{V}$ . If the time constant is measured to be 35.0$\mu \mathrm{s}$ , calculate $(a)$ the total capacitance of the circuit and $(b)$ the time it takes for the voltage across the resistor to reach 16.0 $\mathrm{V}$ after the switch is closed.