Question concerning equivalent capacitance
The 6uF and series 3uF act as a Capacitor Voltage divider.  This is true for DC and AC ( unless they have some unusual leakage)

The smaller 3uF thus rises to 2/3 of 10V  so ...   as Zc is inverse to C 


for 3uF, CV= 2/3 * 10V * 3uF = 20 uC     
for 6uF, CV= 1/3 * 10V * 6uF = 20 uC 
however the 4uF , CV= 4uF * -30V= -120 uC


Total charge = 20uC - 120uC = -100uC
Net Cequiv =   __ ( you do)
Net Vc = - __

Now you can fill in the blanks.
Bottom rail assumed =0V