Three large plates are arranged as shown. How much charge will flow through the key k if it is closed?

Before closing the switch After closing the switchq1+q2=2QVAB=VAC or  q1C1=q2C2  q1q2=C1C2=2  or  q1=2q2Solving, we get  q1=4Q3,  q2=2Q3Charge flown through K is−Q2−(−q1)=−Q2+4Q3=5Q/6