In Fig. $28-32$, the capacitances are $C_{1}=1.0 \mu \mathrm{F}$ and $C_{2}=3.0 \mu \mathrm{F}$ and both capacitors are charged to a potential difference of $\Delta V=100 \mathrm{~V}$ but with opposite polarity as shown. Switches $\mathrm{S}_{1}$, and $\mathrm{S}_{2}$ are now closed. (a) What is now the potential difference between points $a$ and b? What are now the amounts of excess charge on capacitors (b) 1 and $(\mathrm{c}) 2 ?$