College physics, electromagnetism topic, about capacitance, the fourth topic is what to choose for C.
After the first charging, the power of C 1 is 0.008C, and the power of C2 is 0.002c. Because it is reversed, it will neutralize the electricity, and finally the total electricity will become 0.006c.
And because they are parallel, C = C 1+C2 = 0.005438+0f. U=Q/C=600V