Calculate the equivalent capacitance between the points $a$ and $b$ in Figure $\mathrm{P} 26.75$. Note that this is not a simple series or parallel combination. (Hint: Assume a potential difference $\Delta V$ between points $a$ and $b$. Write expressions for $\Delta V_{a b}$ in terms of the charges and capacitances for the various possible pathways from $a$ to $b$, and $\mathrm{rc}-$ quire conservation of charge for those capacitor plates that are connected to each other.)